Systems and methods for controlling a drilling path based on drift estimates

ABSTRACT

In a drilling system, a control system coupled to a drilling rig controls a bottom hole assembly (BHA) to drill a borehole through a geological formation along a drilling path. The control system determines a present position of the BHA and calculates a toolface vector to create a convergence path from the present position of the BHA to a desired target path. The control system also receives geological information and compensates the toolface vector to account for an estimated geologic formation drift. The control system causes at least one control parameter to be modified in order to alter a drilling direction of the BHA based on the calculated toolface vector and transmits the at least one control parameter to the drilling rig to target the BHA in accordance with the calculated toolface vector. The control system iteratively performs this process until convergence with the desired target path is achieved.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/592,226, filed on Oct. 3, 2019, entitled SYSTEMS AND METHODS FORCONTROLLING A DRILLING PATH BASED ON DRIFT ESTIMATES, which is acontinuation of U.S. patent application Ser. No. 15/068,222, filed onMar. 11, 2016, entitled SYSTEM AND METHOD FOR CONTROLLING A DRILLINGPATH BASED ON DRIFT ESTIMATES, now U.S. Pat. No. 10,472,893, issued Nov.12, 2019, which is a continuation of U.S. patent application Ser. No.14/677,648, filed Apr. 2, 2015, entitled SYSTEM AND METHOD FORCONTROLLING A DRILLING PATH BASED ON DRIFT ESTIMATES, now U.S. Pat. No.9,297,205, issued Mar. 29, 2016, which is a continuation-in-part of U.S.patent application Ser. No. 14/095,073, filed Dec. 3, 2013, and entitledSYSTEM AND METHOD FOR DETERMINING INCREMENTAL PROGRESSION BETWEEN SURVEYPOINTS WHILE DRILLING, now U.S. Pat. No. 9,347,308, issued May 24, 2016,which is a continuation of U.S. patent application Ser. No. 13/530,298,filed Jun. 22, 2012, and entitled SYSTEM AND METHOD FOR DETERMININGINCREMENTAL PROGRESSION BETWEEN SURVEY POINTS WHILE DRILLING, now U.S.Pat. No. 8,596,385, issued Dec. 3, 2013, which is a continuation-in-partof U.S. patent application Ser. No. 13/334,370, filed on Dec. 22, 2011,and entitled SYSTEM AND METHOD FOR SURFACE STEERABLE DRILLING, now U.S.Pat. No. 8,210,283, issued Jul. 3, 2013, the specifications of which areincorporated by reference herein in their entirety.

TECHNICAL FIELD

This application is directed to the creation of wells, such as oilwells, and more particularly to the planning and drilling of such wells.

SUMMARY

The present invention, as disclosed and described herein, comprises amethod for drilling. A surface steerable system coupled to a drillingrig receives BHA information from a bottom hole assembly (BHA) locatedin a borehole. The BHA information corresponds to a first location ofthe BHA with respect to a target drilling path and geological formationdrift information. The surface steerable system calculates a toolfacevector to create a convergence path from the first location of the BHAto the target drilling path that accounts for geological formation driftdefined by the geological formation drift information such that the BHAwill converge with the target drilling path by drilling in accordancewith the toolface vector. The surface steerable system causes at leastone control parameter to be modified in order to alter a drillingdirection of the BHA based on the calculated toolface vector andtransmits the at least one control parameter to the drilling rig totarget the BHA in accordance with the calculated toolface vector.

BACKGROUND

Drilling a borehole for the extraction of minerals has become anincreasingly complicated operation due to the increased depth andcomplexity of many boreholes, including the complexity added bydirectional drilling. Drilling is an expensive operation and errors indrilling add to the cost and, in some cases, drilling errors maypermanently lower the output of a well for years into the future.Current technologies and methods do not adequately address thecomplicated nature of drilling. Accordingly, what is needed are a systemand method to improve drilling operations and minimize drilling errors.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding, reference is now made to thefollowing description taken in conjunction with the accompanyingDrawings in which:

FIG. 1A illustrates one embodiment of a drilling environment in which asurface steerable system may operate;

FIG. 1B illustrates one embodiment of a more detailed portion of thedrilling environment of FIG. 1A;

FIG. 1C illustrates one embodiment of a more detailed portion of thedrilling environment of FIG. 1B;

FIG. 2A illustrates one embodiment of the surface steerable system ofFIG. 1A and how information may flow to and from the system;

FIG. 2B illustrates one embodiment of a display that may be used withthe surface steerable system of FIG. 2A;

FIG. 3 illustrates one embodiment of a drilling environment that doesnot have the benefit of the surface steerable system of FIG. 2A andpossible communication channels within the environment;

FIG. 4 illustrates one embodiment of a drilling environment that has thebenefit of the surface steerable system of FIG. 2A and possiblecommunication channels within the environment;

FIG. 5 illustrates one embodiment of data flow that may be supported bythe surface steerable system of FIG. 2A;

FIG. 6 illustrates one embodiment of a method that may be executed bythe surface steerable system of FIG. 2A;

FIG. 7A illustrates a more detailed embodiment of the method of FIG. 6;

FIG. 7B illustrates a more detailed embodiment of the method of FIG. 6;

FIG. 7C illustrates one embodiment of a convergence plan diagram withmultiple convergence paths;

FIG. 8A illustrates a more detailed embodiment of a portion of themethod of FIG. 7B;

FIG. 8B illustrates a more detailed embodiment of a portion of themethod of FIG. 6;

FIG. 8C illustrates a more detailed embodiment of a portion of themethod of FIG. 6;

FIG. 8D illustrates a more detailed embodiment of a portion of themethod of FIG. 6;

FIG. 9 illustrates one embodiment of a system architecture that may beused for the surface steerable system of FIG. 2A;

FIG. 10 illustrates one embodiment of a more detailed portion of thesystem architecture of FIG. 9;

FIG. 11 illustrates one embodiment of a guidance control loop that maybe used within the system architecture of FIG. 9;

FIG. 12 illustrates one embodiment of an autonomous control loop thatmay be used within the system architecture of FIG. 9;

FIG. 13 illustrates one embodiment of a computer system that may be usedwithin the surface steerable system of FIG. 2A;

FIGS. 14A-14D illustrate embodiments of a portion of the drillingenvironment of FIG. 1B;

FIG. 14E illustrates FIGS. 14B-14D overlaid on one another;

FIG. 15 illustrates one embodiment of a three-dimensional boreholespace.

FIG. 16 illustrates one embodiment of a method that may be executed bythe surface steerable system of FIG. 2A to estimate a drill bit positionbetween survey points.

FIG. 17 illustrates one embodiment of a method that represents a portionof the method of FIG. 16 in greater detail.

FIG. 18 illustrates one embodiment of a two-dimensional borehole space.

FIG. 19 illustrates another embodiment of a two-dimensional boreholespace.

FIG. 20 illustrates another embodiment of the two-dimensional boreholespace of FIG. 19.

FIG. 21 illustrates one embodiment of a method that represents a portionof the method of FIG. 16 in greater detail.

FIG. 22 illustrates one embodiment of a method that represents a portionof the method of FIG. 21 in greater detail.

FIG. 23 illustrates one embodiment of a method that may be executed bythe surface steerable system of FIG. 2A.

FIG. 24 illustrates another embodiment of the display of FIG. 2B;

FIG. 25 illustrates one embodiment of a three-dimensional graphillustrating vectors representing information that may be displayed onthe display of FIG. 24;

FIG. 26 illustrates a more particular embodiment of the slide plannerfor determining a drilling path responsive to drift information;

FIG. 27A illustrates a drilling path target selection using a sequenceof slides and rotations;

FIG. 27B illustrates the generation of compensated drill paths based onformation drift;

FIG. 27C illustrates the generation of multiple potential compensateddrill paths; and

FIG. 28 is a flow diagram illustrating the process of compensating adrilling path based on drift information.

DETAILED DESCRIPTION

Referring now to the drawings, wherein like reference numbers are usedherein to designate like elements throughout, the various views andembodiments of a system and method for surface steerable drilling areillustrated and described, and other possible embodiments are described.The figures are not necessarily drawn to scale, and in some instancesthe drawings have been exaggerated and/or simplified in places forillustrative purposes only. One of ordinary skill in the art willappreciate the many possible applications and variations based on thefollowing examples of possible embodiments.

Referring to FIG. 1A, one embodiment of an environment 100 isillustrated with multiple wells 102, 104, 106, 108, and a drilling rig110. In the present example, the wells 102 and 104 are located in aregion 112, the well 106 is located in a region 114, the well 108 islocated in a region 116, and the drilling rig 110 is located in a region118. Each region 112, 114, 116, and 118 may represent a geographic areahaving similar geological formation characteristics. For example, region112 may include particular formation characteristics identified by rocktype, porosity, thickness, and other geological information. Theseformation characteristics affect drilling of the wells 102 and 104.Region 114 may have formation characteristics that are different enoughto be classified as a different region for drilling purposes, and thedifferent formation characteristics affect the drilling of the well 106.Likewise, formation characteristics in the regions 116 and 118 affectthe well 108 and drilling rig 110, respectively.

It is understood the regions 112, 114, 116, and 118 may vary in size andshape depending on the characteristics by which they are identified.Furthermore, the regions 112, 114, 116, and 118 may be sub-regions of alarger region. Accordingly, the criteria by which the regions 112, 114,116, and 118 are identified is less important for purposes of thepresent disclosure than the understanding that each region 112, 114,116, and 118 includes geological characteristics that can be used todistinguish each region from the other regions from a drillingperspective. Such characteristics may be relatively major (e.g., thepresence or absence of an entire rock layer in a given region) or may berelatively minor (e.g., variations in the thickness of a rock layer thatextends through multiple regions).

Accordingly, drilling a well located in the same region as other wells,such as drilling a new well in the region 112 with already existingwells 102 and 104, means the drilling process is likely to face similardrilling issues as those faced when drilling the existing wells in thesame region. For similar reasons, a drilling process performed in oneregion is likely to face issues different from a drilling processperformed in another region. However, even the drilling processes thatcreated the wells 102 and 104 may face different issues during actualdrilling as variations in the formation are likely to occur even in asingle region.

Drilling a well typically involves a substantial amount of humandecision making during the drilling process. For example, geologists anddrilling engineers use their knowledge, experience, and the availableinformation to make decisions on how to plan the drilling operation, howto accomplish the plan, and how to handle issues that arise duringdrilling. However, even the best geologists and drilling engineersperform some guesswork due to the unique nature of each borehole.Furthermore, a directional driller directly responsible for the drillingmay have drilled other boreholes in the same region and so may have somesimilar experience, but it is impossible for a human to mentally trackall the possible inputs and factor those inputs into a decision. Thiscan result in expensive mistakes, as errors in drilling can add hundredsof thousands or even millions of dollars to the drilling cost and, insome cases, drilling errors may permanently lower the output of a well,resulting in substantial long term losses.

In the present example, to aid in the drilling process, each well 102,104, 106, and 108 has corresponding collected data 120, 122, 124, and126, respectively. The collected data may include the geologicalcharacteristics of a particular formation in which the correspondingwell was formed, the attributes of a particular drilling rig, includingthe bottom hole assembly (BHA), and drilling information such asweight-on-bit (WOB), drilling speed, and/or other information pertinentto the formation of that particular borehole. The drilling informationmay be associated with a particular depth or other identifiable markerso that, for example, it is recorded that drilling of the well 102 from1000 feet to 1200 feet occurred at a first ROP through a first rocklayer with a first WOB, while drilling from 1200 feet to 1500 feetoccurred at a second ROP through a second rock layer with a second WOB.The collected data may be used to recreate the drilling process used tocreate the corresponding well 102, 104, 106, or 108 in the particularformation. It is understood that the accuracy with which the drillingprocess can be recreated depends on the level of detail and accuracy ofthe collected data.

The collected data 120, 122, 124, and 126 may be stored in a centralizeddatabase 128 as indicated by lines 130, 132, 134, and 136, respectively,which may represent any wired and/or wireless communication channel(s).The database 128 may be located at a drilling hub (not shown) orelsewhere. Alternatively, the data may be stored on a removable storagemedium that is later coupled to the database 128 in order to store thedata. The collected data 120, 122, 124, and 126 may be stored in thedatabase 128 as formation data 138, equipment data 140, and drillingdata 142 for example. Formation data 138 may include any formationinformation, such as rock type, layer thickness, layer location (e.g.,depth), porosity, gamma readings, etc. Equipment data 140 may includeany equipment information, such as drilling rig configuration (e.g.,rotary table or top drive), bit type, mud composition, etc. Drillingdata 142 may include any drilling information, such as drilling speed,WOB, differential pressure, toolface orientation, etc. The collecteddata may also be identified by well, region, and other criteria, and maybe sortable to enable the data to be searched and analyzed. It isunderstood that many different storage mechanisms may be used to storethe collected data in the database 128.

With additional reference to FIG. 1B, an environment 160 (not to scale)illustrates a more detailed embodiment of a portion of the region 118with the drilling rig 110 located at the surface 162. A drilling planhas been formulated to drill a borehole 164 extending into the ground toa true vertical depth (TVD) 166. The borehole 164 extends through stratalayers 168 and 170, stopping in layer 172, and not reaching underlyinglayers 174 and 176. The borehole 164 may be directed to a target area180 positioned in the layer 172. The target 180 may be a subsurfacepoint or points defined by coordinates or other markers that indicatewhere the borehole 164 is to end or may simply define a depth rangewithin which the borehole 164 is to remain (e.g., the layer 172 itself).It is understood that the target 180 may be any shape and size, and maybe defined in any way. Accordingly, the target 180 may represent anendpoint of the borehole 164 or may extend as far as can berealistically drilled. For example, if the drilling includes ahorizontal component and the goal is to follow the layer 172 as far aspossible, the target may simply be the layer 172 itself and drilling maycontinue until a limit is reached, such as a property boundary or aphysical limitation to the length of the drillstring. A fault 178 hasshifted a portion of each layer downwards. Accordingly, the borehole 164is located in non-shifted layer portions 168A-176A, while portions168B-176B represent the shifted layer portions.

Current drilling techniques frequently involve directional drilling toreach a target, such as the target 180. The use of directional drillinggenerally increases the amount of reserves that can be obtained and alsoincreases production rate, sometimes significantly. For example, thedirectional drilling used to provide the horizontal portion shown inFIG. 1B increases the length of the borehole in the layer 172, which isthe target layer in the present example. Directional drilling may alsobe used alter the angle of the borehole to address faults, such as thefault 178 that has shifted the layer portion 172B. Other uses fordirectional drilling include sidetracking off of an existing well toreach a different target area or a missed target area, drilling aroundabandoned drilling equipment, drilling into otherwise inaccessible ordifficult to reach locations (e.g., under populated areas or bodies ofwater), providing a relief well for an existing well, and increasing thecapacity of a well by branching off and having multiple boreholesextending in different directions or at different vertical positions forthe same well. Directional drilling is often not confined to a straighthorizontal borehole, but may involve staying within a rock layer thatvaries in depth and thickness as illustrated by the layer 172. As such,directional drilling may involve multiple vertical adjustments thatcomplicate the path of the borehole.

With additional reference to FIG. 1C, which illustrates one embodimentof a portion of the borehole 164 of FIG. 1B, the drilling of horizontalwells clearly introduces significant challenges to drilling that do notexist in vertical wells. For example, a substantially horizontal portion192 of the well may be started off of a vertical borehole 190 and onedrilling consideration is the transition from the vertical portion ofthe well to the horizontal portion. This transition is generally a curvethat defines a build up section 194 beginning at the vertical portion(called the kick off point and represented by line 196) and ending atthe horizontal portion (represented by line 198). The change ininclination per measured length drilled is typically referred to as thebuild rate and is often defined in degrees per one hundred feet drilled.For example, the build rate may be 6°/100 ft, indicating that there is asix degree change in inclination for every one hundred feet drilled. Thebuild rate for a particular build up section may remain relativelyconstant or may vary.

The build rate depends on factors such as the formation through whichthe borehole 164 is to be drilled, the trajectory of the borehole 164,the particular pipe and drill collars/BHA components used (e.g., length,diameter, flexibility, strength, mud motor bend setting, and drill bit),the mud type and flow rate, the required horizontal displacement,stabilization, and inclination. An overly aggressive built rate cancause problems such as severe doglegs (e.g., sharp changes in directionin the borehole) that may make it difficult or impossible to run casingor perform other needed tasks in the borehole 164. Depending on theseverity of the mistake, the borehole 164 may require enlarging or thebit may need to be backed out and a new passage formed. Such mistakescost time and money. However, if the built rate is too cautious,significant additional time may be added to the drilling process as itis generally slower to drill a curve than to drill straight.Furthermore, drilling a curve is more complicated and the possibility ofdrilling errors increases (e.g., overshoot and undershoot that may occurtrying to keep the bit on the planned path).

Two modes of drilling, known as rotating and sliding, are commonly usedto form the borehole 164. Rotating, also called rotary drilling, uses atopdrive or rotary table to rotate the drillstring. Rotating is usedwhen drilling is to occur along a straight path. Sliding, also calledsteering, uses a downhole mud motor with an adjustable bent housing anddoes not rotate the drillstring. Instead, sliding uses hydraulic powerto drive the downhole motor and bit. Sliding is used in order to controlwell direction.

To accomplish a slide, the rotation of the drill string is stopped.Based on feedback from measuring equipment such as a MWD tool,adjustments are made to the drill string. These adjustments continueuntil the downhole toolface that indicates the direction of the bend ofthe motor is oriented to the direction of the desired deviation of theborehole. Once the desired orientation is accomplished, pressure isapplied to the drill bit, which causes the drill bit to move in thedirection of deviation. Once sufficient distance and angle have beenbuilt, a transition back to rotating mode is accomplished by rotatingthe drill string. This rotation of the drill string neutralizes thedirectional deviation caused by the bend in the motor as it continuouslyrotates around the centerline of the borehole.

Referring again to FIG. 1A, the formulation of a drilling plan for thedrilling rig 110 may include processing and analyzing the collected datain the database 128 to create a more effective drilling plan.Furthermore, once the drilling has begun, the collected data may be usedin conjunction with current data from the drilling rig 110 to improvedrilling decisions. Accordingly, an on-site controller 144 is coupled tothe drilling rig 110 and may also be coupled to the database 128 via oneor more wired and/or wireless communication channel(s) 146. Other inputs148 may also be provided to the on-site controller 144. In someembodiments, the on-site controller 144 may operate as a stand-alonedevice with the drilling rig 110. For example, the on-site controller144 may not be communicatively coupled to the database 128. Althoughshown as being positioned near or at the drilling rig 110 in the presentexample, it is understood that some or all components of the on-sitecontroller 144 may be distributed and located elsewhere in otherembodiments.

The on-site controller 144 may form all or part of a surface steerablesystem. The database 128 may also form part of the surface steerablesystem. As will be described in greater detail below, the surfacesteerable system may be used to plan and control drilling operationsbased on input information, including feedback from the drilling processitself. The surface steerable system may be used to perform suchoperations as receiving drilling data representing a drill path andother drilling parameters, calculating a drilling solution for the drillpath based on the received data and other available data (e.g., rigcharacteristics), implementing the drilling solution at the drilling rig110, monitoring the drilling process to gauge whether the drillingprocess is within a defined margin of error of the drill path, and/orcalculating corrections for the drilling process if the drilling processis outside of the margin of error.

Referring to FIG. 2A, a diagram 200 illustrates one embodiment ofinformation flow for a surface steerable system 201 from the perspectiveof the on-site controller 144 of FIG. 1A. In the present example, thedrilling rig 110 of FIG. 1A includes drilling equipment 216 used toperform the drilling of a borehole, such as top drive or rotary driveequipment that couples to the drill string and BHA and is configured torotate the drill string and apply pressure to the drill bit. Thedrilling rig 110 may include control systems such as a WOB/differentialpressure control system 208, a positional/rotary control system 210, anda fluid circulation control system 212. The control systems 208, 210,and 212 may be used to monitor and change drilling rig settings, such asthe WOB and/or differential pressure to alter the ROP or the radialorientation of the toolface, change the flow rate of drilling mud, andperform other operations.

The drilling rig 110 may also include a sensor system 214 for obtainingsensor data about the drilling operation and the drilling rig 110,including the downhole equipment. For example, the sensor system 214 mayinclude measuring while drilling (MWD) and/or logging while drilling(LWD) components for obtaining information, such as toolface and/orformation logging information, that may be saved for later retrieval,transmitted with a delay or in real time using any of variouscommunication means (e.g., wireless, wireline, or mud pulse telemetry),or otherwise transferred to the on-site controller 144. Such informationmay include information related to hole depth, bit depth, inclination,azimuth, true vertical depth, gamma count, standpipe pressure, mud flowrate, rotary rotations per minute (RPM), bit speed, ROP, WOB, and/orother information. It is understood that all or part of the sensorsystem 214 may be incorporated into one or more of the control systems208, 210, and 212, and/or in the drilling equipment 216. As the drillingrig 110 may be configured in many different ways, it is understood thatthese control systems may be different in some embodiments, and may becombined or further divided into various subsystems.

The on-site controller 144 receives input information 202. The inputinformation 202 may include information that is pre-loaded, received,and/or updated in real time. The input information 202 may include awell plan, regional formation history, one or more drilling engineerparameters, MWD tool face/inclination information, LWD gamma/resistivityinformation, economic parameters, reliability parameters, and/or otherdecision guiding parameters. Some of the inputs, such as the regionalformation history, may be available from a drilling hub 216, which mayinclude the database 128 of FIG. 1A and one or more processors (notshown), while other inputs may be accessed or uploaded from othersources. For example, a web interface may be used to interact directlywith the on-site controller 144 to upload the well plan and/or drillingengineer parameters. The input information 202 feeds into the on-sitecontroller 144 and, after processing by the on-site controller 144,results in control information 204 that is output to the drilling rig110 (e.g., to the control systems 208, 210, and 212). The drilling rig110 (e.g., via the systems 208, 210, 212, and 214) provides feedbackinformation 206 to the on-site controller 144. The feedback information206 then serves as input to the on-site controller 144, enabling theon-site controller 144 to verify that the current control information isproducing the desired results or to produce new control information forthe drilling rig 110.

The on-site controller 144 also provides output information 203. As willbe described later in greater detail, the output information 203 may bestored in the on-site controller 144 and/or sent offsite (e.g., to thedatabase 128). The output information 203 may be used to provide updatesto the database 128, as well as provide alerts, request decisions, andconvey other data related to the drilling process.

Referring to FIG. 2B, one embodiment of a display 250 that may beprovided by the on-site controller 144 is illustrated. The display 250provides many different types of information in an easily accessibleformat. For example, the display 250 may be a viewing screen (e.g., amonitor) that is coupled to or forms part of the on-site controller 144.

The display 250 provides visual indicators such as a hole depthindicator 252, a bit depth indicator 254, a GAMMA indicator 256, aninclination indicator 258, an azimuth indicator 260, and a TVD indicator262. Other indicators may also be provided, including a ROP indicator264, a mechanical specific energy (MSE) indicator 266, a differentialpressure indicator 268, a standpipe pressure indicator 270, a flow rateindicator 272, a rotary RPM indicator 274, a bit speed indicator 276,and a WOB indicator 278.

Some or all of the indicators 264, 266, 268, 270, 272, 274, 276, and/or278 may include a marker representing a target value. For purposes ofexample, markers are set as the following values, but it is understoodthat any desired target value may be representing. For example, the ROPindicator 264 may include a marker 265 indicating that the target valueis fifty ft/hr. The MSE indicator 266 may include a marker 267indicating that the target value is thirty-seven ksi. The differentialpressure indicator 268 may include a marker 269 indicating that thetarget value is two hundred psi. The ROP indicator 264 may include amarker 265 indicating that the target value is fifty ft/hr. Thestandpipe pressure indicator 270 may have no marker in the presentexample. The flow rate indicator 272 may include a marker 273 indicatingthat the target value is five hundred gpm. The rotary RPM indicator 274may include a marker 275 indicating that the target value is zero RPM(due to sliding). The bit speed indicator 276 may include a marker 277indicating that the target value is one hundred and fifty RPM. The WOBindicator 278 may include a marker 279 indicating that the target valueis ten klbs. Although only labeled with respect to the indicator 264,each indicator may include a colored band 263 or another marking toindicate, for example, whether the respective gauge value is within asafe range (e.g., indicated by a green color), within a caution range(e.g., indicated by a yellow color), or within a danger range (e.g.,indicated by a red color). Although not shown, in some embodiments,multiple markers may be present on a single indicator. The markers mayvary in color and/or size.

A log chart 280 may visually indicate depth versus one or moremeasurements (e.g., may represent log inputs relative to a progressingdepth chart). For example, the log chart 280 may have a y-axisrepresenting depth and an x-axis representing a measurement such asGAMMA count 281 (as shown), ROP 283 (e.g., empirical ROP and normalizedROP), or resistivity. An autopilot button 282 and an oscillate button284 may be used to control activity. For example, the autopilot button282 may be used to engage or disengage an autopilot, while the oscillatebutton 284 may be used to directly control oscillation of the drillstring or engage/disengage an external hardware device or controller viasoftware and/or hardware.

A circular chart 286 may provide current and historical toolfaceorientation information (e.g., which way the bend is pointed). Forpurposes of illustration, the circular chart 286 represents threehundred and sixty degrees. A series of circles within the circular chart286 may represent a timeline of toolface orientations, with the sizes ofthe circles indicating the temporal position of each circle. Forexample, larger circles may be more recent than smaller circles, so thelargest circle 288 may be the newest reading and the smallest circle 289may be the oldest reading. In other embodiments, the circles mayrepresent the energy and/or progress made via size, color, shape, anumber within a circle, etc. For example, the size of a particularcircle may represent an accumulation of orientation and progress for theperiod of time represented by the circle. In other embodiments,concentric circles representing time (e.g., with the outside of thecircular chart 286 being the most recent time and the center point beingthe oldest time) may be used to indicate the energy and/or progress(e.g., via color and/or patterning such as dashes or dots rather than asolid line).

The circular chart 286 may also be color coded, with the color codingexisting in a band 290 around the circular chart 286 or positioned orrepresented in other ways. The color coding may use colors to indicateactivity in a certain direction. For example, the color red may indicatethe highest level of activity, while the color blue may indicate thelowest level of activity. Furthermore, the arc range in degrees of acolor may indicate the amount of deviation. Accordingly, a relativelynarrow (e.g., thirty degrees) arc of red with a relatively broad (e.g.,three hundred degrees) arc of blue may indicate that most activity isoccurring in a particular toolface orientation with little deviation.For purposes of illustration, the color blue extends from approximately22-337 degrees, the color green extends from approximately 15-22 degreesand 337-345 degrees, the color yellow extends a few degrees around the13 and 345 degree marks, and the color red extends from approximately347-10 degrees. Transition colors or shades may be used with, forexample, the color orange marking the transition between red and yellowand/or a light blue marking the transition between blue and green.

This color coding enables the display 250 to provide an intuitivesummary of how narrow the standard deviation is and how much of theenergy intensity is being expended in the proper direction. Furthermore,the center of energy may be viewed relative to the target. For example,the display 250 may clearly show that the target is at ninety degreesbut the center of energy is at forty-five degrees.

Other indicators may be present, such as a slide indicator 292 toindicate how much time remains until a slide occurs and/or how much timeremains for a current slide. For example, the slide indicator mayrepresent a time, a percentage (e.g., current slide is fifty-six percentcomplete), a distance completed, and/or a distance remaining. The slideindicator 292 may graphically display information using, for example, acolored bar 293 that increases or decreases with the slide's progress.In some embodiments, the slide indicator may be built into the circularchart 286 (e.g., around the outer edge with an increasing/decreasingband), while in other embodiments the slide indicator may be a separateindicator such as a meter, a bar, a gauge, or another indicator type.

An error indicator 294 may be present to indicate a magnitude and/or adirection of error. For example, the error indicator 294 may indicatethat the estimated drill bit position is a certain distance from theplanned path, with a location of the error indicator 294 around thecircular chart 286 representing the heading. For example, FIG. 2Billustrates an error magnitude of fifteen feet and an error direction offifteen degrees. The error indicator 294 may be any color but is red forpurposes of example. It is understood that the error indicator 294 maypresent a zero if there is no error and/or may represent that the bit ison the path in other ways, such as being a green color. Transitioncolors, such as yellow, may be used to indicate varying amounts oferror. In some embodiments, the error indicator 294 may not appearunless there is an error in magnitude and/or direction. A marker 296 mayindicate an ideal slide direction. Although not shown, other indicatorsmay be present, such as a bit life indicator to indicate an estimatedlifetime for the current bit based on a value such as time and/ordistance.

It is understood that the display 250 may be arranged in many differentways. For example, colors may be used to indicate normal operation,warnings, and problems. In such cases, the numerical indicators maydisplay numbers in one color (e.g., green) for normal operation, may useanother color (e.g., yellow) for warnings, and may use yet another color(e.g., red) if a serious problem occurs. The indicators may also flashor otherwise indicate an alert. The gauge indicators may include colors(e.g., green, yellow, and red) to indicate operational conditions andmay also indicate the target value (e.g., an ROP of 100 ft/hr). Forexample, the ROP indicator 264 may have a green bar to indicate a normallevel of operation (e.g., from 10-300 ft/hr), a yellow bar to indicate awarning level of operation (e.g., from 300-360 ft/hr), and a red bar toindicate a dangerous or otherwise out of parameter level of operation(e.g., from 360-390 ft/hr). The ROP indicator 264 may also display amarker at 100 ft/hr to indicate the desired target ROP.

Furthermore, the use of numeric indicators, gauges, and similar visualdisplay indicators may be varied based on factors such as theinformation to be conveyed and the personal preference of the viewer.Accordingly, the display 250 may provide a customizable view of variousdrilling processes and information for a particular individual involvedin the drilling process. For example, the surface steerable system 201may enable a user to customize the display 250 as desired, althoughcertain features (e.g., standpipe pressure) may be locked to preventremoval. This locking may prevent a user from intentionally oraccidentally removing important drilling information from the display.Other features may be set by preference. Accordingly, the level ofcustomization and the information shown by the display 250 may becontrolled based on who is viewing the display and their role in thedrilling process.

Referring again to FIG. 2A, it is understood that the level ofintegration between the on-site controller 144 and the drilling rig 110may depend on such factors as the configuration of the drilling rig 110and whether the on-site controller 144 is able to fully support thatconfiguration. One or more of the control systems 208, 210, and 212 maybe part of the on-site controller 144, may be third-party systems,and/or may be part of the drilling rig 110. For example, an olderdrilling rig 110 may have relatively few interfaces with which theon-site controller 144 is able to interact. For purposes ofillustration, if a knob must be physically turned to adjust the WOB onthe drilling rig 110, the on-site controller 144 will not be able todirectly manipulate the knob without a mechanical actuator. If such anactuator is not present, the on-site controller 144 may output thesetting for the knob to a screen, and an operator may then turn the knobbased on the setting. Alternatively, the on-site controller 144 may bedirectly coupled to the knob's electrical wiring.

However, a newer or more sophisticated drilling rig 110, such as a rigthat has electronic control systems, may have interfaces with which theon-site controller 144 can interact for direct control. For example, anelectronic control system may have a defined interface and the on-sitecontroller 144 may be configured to interact with that definedinterface. It is understood that, in some embodiments, direct controlmay not be allowed even if possible. For example, the on-site controller144 may be configured to display the setting on a screen for approval,and may then send the setting to the appropriate control system onlywhen the setting has been approved.

Referring to FIG. 3, one embodiment of an environment 300 illustratesmultiple communication channels (indicated by arrows) that are commonlyused in existing directional drilling operations that do not have thebenefit of the surface steerable system 201 of FIG. 2A. Thecommunication channels couple various individuals involved in thedrilling process. The communication channels may support telephonecalls, emails, text messages, faxes, data transfers (e.g., filetransfers over networks), and other types of communications.

The individuals involved in the drilling process may include a drillingengineer 302, a geologist 304, a directional driller 306, a tool pusher308, a driller 310, and a rig floor crew 312. One or more companyrepresentatives (e.g., company men) 314 may also be involved. Theindividuals may be employed by different organizations, which canfurther complicate the communication process. For example, the drillingengineer 302, geologist 304, and company man 314 may work for anoperator, the directional driller 306 may work for a directionaldrilling service provider, and the tool pusher 308, driller 310, and rigfloor crew 312 may work for a rig service provider.

The drilling engineer 302 and geologist 304 are often located at alocation remote from the drilling rig (e.g., in a home office/drillinghub). The drilling engineer 302 may develop a well plan 318 and may makedrilling decisions based on drilling rig information. The geologist 304may perform such tasks as formation analysis based on seismic, gamma,and other data. The directional driller 306 is generally located at thedrilling rig and provides instructions to the driller 310 based on thecurrent well plan and feedback from the drilling engineer 302. Thedriller 310 handles the actual drilling operations and may rely on therig floor crew 312 for certain tasks. The tool pusher 308 may be incharge of managing the entire drilling rig and its operation.

The following is one possible example of a communication process withinthe environment 300, although it is understood that many communicationprocesses may be used. The use of a particular communication process maydepend on such factors as the level of control maintained by variousgroups within the process, how strictly communication channels areenforced, and similar factors. In the present example, the directionaldriller 306 uses the well plan 318 to provide drilling instructions tothe driller 310. The driller 310 controls the drilling using controlsystems such as the control systems 208, 210, and 212 of FIG. 2A. Duringdrilling, information from sensor equipment such as downhole MWDequipment 316 and/or rig sensors 320 may indicate that a formation layerhas been reached twenty feet higher than expected by the geologist 304.This information is passed back to the drilling engineer 302 and/orgeologist 304 through the company man 314, and may pass through thedirectional driller 306 before reaching the company man 314.

The drilling engineer 302/well planner (not shown), either alone or inconjunction with the geologist 306, may modify the well plan 318 or makeother decisions based on the received information. The modified wellplan and/or other decisions may or may not be passed through the companyman 314 to the directional driller 306, who then tells the driller 310how to drill. The driller 310 may modify equipment settings (e.g.,toolface orientation) and, if needed, pass orders on to the rig floorcrew 312. For example, a change in WOB may be performed by the driller310 changing a setting, while a bit trip may require the involvement ofthe rig floor crew 312. Accordingly, the level of involvement ofdifferent individuals may vary depending on the nature of the decisionto be made and the task to be performed. The proceeding example may bemore complex than described. Multiple intermediate individuals may beinvolved and, depending on the communication chain, some instructionsmay be passed through the tool pusher 308.

The environment 300 presents many opportunities for communicationbreakdowns as information is passed through the various communicationchannels, particularly given the varying types of communication that maybe used. For example, verbal communications via phone may bemisunderstood and, unless recorded, provide no record of what was said.Furthermore, accountability may be difficult or impossible to enforce assomeone may provide an authorization but deny it or claim that theymeant something else. Without a record of the information passingthrough the various channels and the authorizations used to approvechanges in the drilling process, communication breakdowns can bedifficult to trace and address. As many of the communication channelsillustrated in FIG. 3 pass information through an individual to otherindividuals (e.g., an individual may serve as an information conduitbetween two or more other individuals), the risk of breakdown increasesdue to the possibility that errors may be introduced in the information.

Even if everyone involved does their part, drilling mistakes may beamplified while waiting for an answer. For example, a message may besent to the geologist 306 that a formation layer seems to be higher thanexpected, but the geologist 306 may be asleep. Drilling may continuewhile waiting for the geologist 306 and the continued drilling mayamplify the error. Such errors can cost hundreds of thousands ormillions of dollars. However, the environment 300 provides no way todetermine if the geologist 304 has received the message and no way toeasily notify the geologist 304 or to contact someone else when there isno response within a defined period of time. Even if alternate contactsare available, such communications may be cumbersome and there may bedifficulty in providing all the information that the alternate wouldneed for a decision.

Referring to FIG. 4, one embodiment of an environment 400 illustratescommunication channels that may exist in a directional drillingoperation having the benefit of the surface steerable system 201 of FIG.2A. In the present example, the surface steerable system 201 includesthe drilling hub 216, which includes the regional database 128 of FIG.1A and processing unit(s) 404 (e.g., computers). The drilling hub 216also includes communication interfaces (e.g., web portals) 406 that maybe accessed by computing devices capable of wireless and/or wirelinecommunications, including desktop computers, laptops, tablets, smartphones, and personal digital assistants (PDAs). The on-site controller144 includes one or more local databases 410 (where “local” is from theperspective of the on-site controller 144) and processing unit(s) 412.

The drilling hub 216 is remote from the on-site controller 144, andvarious individuals associated with the drilling operation interacteither through the drilling hub 216 or through the on-site controller144. In some embodiments, an individual may access the drilling projectthrough both the drilling hub 216 and on-site controller 144. Forexample, the directional driller 306 may use the drilling hub 216 whennot at the drilling site and may use the on-site controller 144 when atthe drilling site.

The drilling engineer 302 and geologist 304 may access the surfacesteerable system 201 remotely via the portal 406 and set variousparameters such as rig limit controls. Other actions may also besupported, such as granting approval to a request by the directionaldriller 306 to deviate from the well plan and evaluating the performanceof the drilling operation. The directional driller 306 may be locatedeither at the drilling rig 110 or off-site. Being off-site (e.g., at thedrilling hub 216 or elsewhere) enables a single directional driller tomonitor multiple drilling rigs. When off-site, the directional driller306 may access the surface steerable system 201 via the portal 406. Whenon-site, the directional driller 306 may access the surface steerablesystem via the on-site controller 144.

The driller 310 may get instructions via the on-site controller 144,thereby lessening the possibly of miscommunication and ensuring that theinstructions were received. Although the tool pusher 308, rig floor crew312, and company man 314 are shown communicating via the driller 310, itis understood that they may also have access to the on-site controller144. Other individuals, such as a MWD hand 408, may access the surfacesteerable system 201 via the drilling hub 216, the on-site controller144, and/or an individual such as the driller 310.

As illustrated in FIG. 4, many of the individuals involved in a drillingoperation may interact through the surface steerable system 201. Thisenables information to be tracked as it is handled by the variousindividuals involved in a particular decision. For example, the surfacesteerable system 201 may track which individual submitted information(or whether information was submitted automatically), who viewed theinformation, who made decisions, when such events occurred, and similarinformation-based issues. This provides a complete record of howparticular information propagated through the surface steerable system201 and resulted in a particular drilling decision. This also providesrevision tracking as changes in the well plan occur, which in turnenables entire decision chains to be reviewed. Such reviews may lead toimproved decision making processes and more efficient responses toproblems as they occur.

In some embodiments, documentation produced using the surface steerablesystem 201 may be synchronized and/or merged with other documentation,such as that produced by third party systems such as the WellViewproduct produced by Peloton Computer Enterprises Ltd. of Calgary,Canada. In such embodiments, the documents, database files, and otherinformation produced by the surface steerable system 201 is synchronizedto avoid such issues as redundancy, mismatched file versions, and othercomplications that may occur in projects where large numbers ofdocuments are produced, edited, and transmitted by a relatively largenumber of people.

The surface steerable system 201 may also impose mandatory informationformats and other constraints to ensure that predefined criteria aremet. For example, an electronic form provided by the surface steerablesystem 201 in response to a request for authorization may require thatsome fields are filled out prior to submission. This ensures that thedecision maker has the relevant information prior to making thedecision. If the information for a required field is not available, thesurface steerable system 201 may require an explanation to be enteredfor why the information is not available (e.g., sensor failure).Accordingly, a level of uniformity may be imposed by the surfacesteerable system 201, while exceptions may be defined to enable thesurface steerable system 201 to handle various scenarios.

The surface steerable system 201 may also send alerts (e.g., email ortext alerts) to notify one or more individuals of a particular problem,and the recipient list may be customized based on the problem.Furthermore, contact information may be time-based, so the surfacesteerable system 201 may know when a particular individual is available.In such situations, the surface steerable system 201 may automaticallyattempt to communicate with an available contact rather than waiting fora response from a contact that is likely not available.

As described previously, the surface steerable system 201 may present acustomizable display of various drilling processes and information for aparticular individual involved in the drilling process. For example, thedrilling engineer 302 may see a display that presents informationrelevant to the drilling engineer's tasks, and the geologist 304 may seea different display that includes additional and/or more detailedformation information. This customization enables each individual toreceive information needed for their particular role in the drillingprocess while minimizing or eliminating unnecessary information.

Referring to FIG. 5, one embodiment of an environment 500 illustratesdata flow that may be supported by the surface steerable system 201 ofFIG. 2A. The data flow 500 begins at block 502 and may move through twobranches, although some blocks in a branch may not occur before otherblocks in the other branch. One branch involves the drilling hub 216 andthe other branch involves the on-site controller 144 at the drilling rig110.

In block 504, a geological survey is performed. The survey results arereviewed by the geologist 304 and a formation report 506 is produced.The formation report 506 details formation layers, rock type, layerthickness, layer depth, and similar information that may be used todevelop a well plan. In block 508, a well plan is developed by a wellplanner 524 and/or the drilling engineer 302 based on the formationreport and information from the regional database 128 at the drillinghub 216. Block 508 may include selection of a BHA and the setting ofcontrol limits. The well plan is stored in the database 128. Thedrilling engineer 302 may also set drilling operation parameters in step510 that are also stored in the database 128.

In the other branch, the drilling rig 110 is constructed in block 512.At this point, as illustrated by block 526, the well plan, BHAinformation, control limits, historical drilling data, and controlcommands may be sent from the database 128 to the local database 410.Using the receiving information, the directional driller 306 inputsactual BHA parameters in block 514. The company man 314 and/or thedirectional driller 306 may verify performance control limits in block516, and the control limits are stored in the local database 410 of theon-site controller 144. The performance control limits may includemultiple levels such as a warning level and a critical levelcorresponding to no action taken within feet/minutes.

Once drilling begins, a diagnostic logger (described later in greaterdetail) 520 that is part of the on-site controller 144 logs informationrelated to the drilling such as sensor information and maneuvers andstores the information in the local database 410 in block 526. Theinformation is sent to the database 128. Alerts are also sent from theon-site controller 144 to the drilling hub 216. When an alert isreceived by the drilling hub 216, an alert notification 522 is sent todefined individuals, such as the drilling engineer 302, geologist 304,and company man 314. The actual recipient may vary based on the contentof the alert message or other criteria. The alert notification 522 mayresult in the well plan and the BHA information and control limits beingmodified in block 508 and parameters being modified in block 510. Thesemodifications are saved to the database 128 and transferred to the localdatabase 410. The BHA may be modified by the directional driller 306 inblock 518, and the changes propagated through blocks 514 and 516 withpossible updated control limits. Accordingly, the surface steerablesystem 201 may provide a more controlled flow of information than mayoccur in an environment without such a system.

The flow charts described herein illustrate various exemplary functionsand operations that may occur within various environments. Accordingly,these flow charts are not exhaustive and that various steps may beexcluded to clarify the aspect being described. For example, it isunderstood that some actions, such as network authentication processes,notifications, and handshakes, may have been performed prior to thefirst step of a flow chart. Such actions may depend on the particulartype and configuration of communications engaged in by the on-sitecontroller 144 and/or drilling hub 216. Furthermore, other communicationactions may occur between illustrated steps or simultaneously withillustrated steps.

The surface steerable system 201 includes large amounts of dataspecifically related to various drilling operations as stored indatabases such as the databases 128 and 410. As described with respectto FIG. 1A, this data may include data collected from many differentlocations and may correspond to many different drilling operations. Thedata stored in the database 128 and other databases may be used for avariety of purposes, including data mining and analytics, which may aidin such processes as equipment comparisons, drilling plan formulation,convergence planning, recalibration forecasting, and self-tuning (e.g.,drilling performance optimization). Some processes, such as equipmentcomparisons, may not be performed in real time using incoming data,while others, such as self-tuning, may be performed in real time or nearreal time. Accordingly, some processes may be executed at the drillinghub 216, other processes may be executed at the on-site controller 144,and still other processes may be executed by both the drilling hub 216and the on-site controller 144 with communications occurring before,during, and/or after the processes are executed. As described below invarious examples, some processes may be triggered by events (e.g.,recalibration forecasting) while others may be ongoing (e.g.,self-tuning).

For example, in equipment comparison, data from different drillingoperations (e.g., from drilling the wells 102, 104, 106, and 108) may benormalized and used to compare equipment wear, performance, and similarfactors. For example, the same bit may have been used to drill the wells102 and 106, but the drilling may have been accomplished using differentparameters (e.g., rotation speed and WOB). By normalizing the data, thetwo bits can be compared more effectively. The normalized data may befurther processed to improve drilling efficiency by identifying whichbits are most effective for particular rock layers, which drillingparameters resulted in the best ROP for a particular formation, ROPversus reliability tradeoffs for various bits in various rock layers,and similar factors. Such comparisons may be used to select a bit foranother drilling operation based on formation characteristics or othercriteria. Accordingly, by mining and analyzing the data available viathe surface steerable system 201, an optimal equipment profile may bedeveloped for different drilling operations. The equipment profile maythen be used when planning future wells or to increase the efficiency ofa well currently being drilled. This type of drilling optimization maybecome increasingly accurate as more data is compiled and analyzed.

In drilling plan formulation, the data available via the surfacesteerable system 201 may be used to identify likely formationcharacteristics and to select an appropriate equipment profile. Forexample, the geologist 304 may use local data obtained from the plannedlocation of the drilling rig 110 in conjunction with regional data fromthe database 128 to identify likely locations of the layers 168A-176A(FIG. 1B). Based on that information, the drilling engineer 302 cancreate a well plan that will include the build curve of FIG. 1C.

Referring to FIG. 6, a method 600 illustrates one embodiment of anevent-based process that may be executed by the on-site controller 144of FIG. 2A. For example, software instructions needed to execute themethod 600 may be stored on a computer readable storage medium of theon-site controller 144 and then executed by the processor 412 that iscoupled to the storage medium and is also part of the on-site controller144.

In step 602, the on-site controller 144 receives inputs, such as aplanned path for a borehole, formation information for the borehole,equipment information for the drilling rig, and a set of costparameters. The cost parameters may be used to guide decisions made bythe on-site controller 144 as will be explained in greater detail below.The inputs may be received in many different ways, including receivingdocument (e.g., spreadsheet) uploads, accessing a database (e.g., thedatabase 128 of FIG. 1A), and/or receiving manually entered data.

In step 604, the planned path, the formation information, the equipmentinformation, and the set of cost parameters are processed to producecontrol parameters (e.g., the control information 204 of FIG. 2A) forthe drilling rig 110. The control parameters may define the settings forvarious drilling operations that are to be executed by the drilling rig110 to form the borehole, such as WOB, flow rate of mud, toolfaceorientation, and similar settings. In some embodiments, the controlparameters may also define particular equipment selections, such as aparticular bit. In the present example, step 604 is directed to defininginitial control parameters for the drilling rig 110 prior to thebeginning of drilling, but it is understood that step 604 may be used todefine control parameters for the drilling rig 110 even after drillinghas begun. For example, the on-site controller 144 may be put in placeprior to drilling or may be put in place after drilling has commenced,in which case the method 600 may also receive current boreholeinformation in step 602.

In step 606, the control parameters are output for use by the drillingrig 110. In embodiments where the on-site controller 144 is directlycoupled to the drilling rig 110, outputting the control parameters mayinclude sending the control parameters directly to one or more of thecontrol systems of the drilling rig 110 (e.g., the control systems 210,212, and 214). In other embodiments, outputting the control parametersmay include displaying the control parameters on a screen, printing thecontrol parameters, and/or copying them to a storage medium (e.g., aUniversal Serial Bus (USB) drive) to be transferred manually.

In step 608, feedback information received from the drilling rig 110(e.g., from one or more of the control systems 210, 212, and 214 and/orsensor system 216) is processed. The feedback information may providethe on-site controller 144 with the current state of the borehole (e.g.,depth and inclination), the drilling rig equipment, and the drillingprocess, including an estimated position of the bit in the borehole. Theprocessing may include extracting desired data from the feedbackinformation, normalizing the data, comparing the data to desired orideal parameters, determining whether the data is within a definedmargin of error, and/or any other processing steps needed to make use ofthe feedback information.

In step 610, the on-site controller 144 may take action based on theoccurrence of one or more defined events. For example, an event maytrigger a decision on how to proceed with drilling in the most costeffective manner. Events may be triggered by equipment malfunctions,path differences between the measured borehole and the planned borehole,upcoming maintenance periods, unexpected geological readings, and anyother activity or non-activity that may affect drilling the borehole. Itis understood that events may also be defined for occurrences that havea less direct impact on drilling, such as actual or predicted laborshortages, actual or potential licensing issues for mineral rights,actual or predicted political issues that may impact drilling, andsimilar actual or predicted occurrences. Step 610 may also result in noaction being taken if, for example, drilling is occurring without anyissues and the current control parameters are satisfactory.

An event may be defined in the received inputs of step 602 or definedlater. Events may also be defined on site using the on-site controller144. For example, if the drilling rig 110 has a particular mechanicalissue, one or more events may be defined to monitor that issue in moredetail than might ordinarily occur. In some embodiments, an event chainmay be implemented where the occurrence of one event triggers themonitoring of another related event. For example, a first event maytrigger a notification about a potential problem with a piece ofequipment and may also activate monitoring of a second event. Inaddition to activating the monitoring of the second event, thetriggering of the first event may result in the activation of additionaloversight that involves, for example, checking the piece of equipmentmore frequently or at a higher level of detail. If the second eventoccurs, the equipment may be shut down and an alarm sounded, or otheractions may be taken. This enables different levels of monitoring anddifferent levels of responses to be assigned independently if needed.

Referring to FIG. 7A, a method 700 illustrates a more detailedembodiment of the method 600 of FIG. 6, particularly of step 610. Assteps 702, 704, 706, and 708 are similar or identical to steps 602, 604,606, and 608, respectively, of FIG. 6, they are not described in detailin the present embodiment. In the present example, the action of step610 of FIG. 6 is based on whether an event has occurred and the actionneeded if the event has occurred.

Accordingly, in step 710, a determination is made as to whether an eventhas occurred based on the inputs of steps 702 and 708. If no event hasoccurred, the method 700 returns to step 708. If an event has occurred,the method 700 moves to step 712, where calculations are performed basedon the information relating to the event and at least one costparameter. It is understood that additional information may be obtainedand/or processed prior to or as part of step 712 if needed. For example,certain information may be used to determine whether an event hasoccurred, and additional information may then be retrieved and processedto determine the particulars of the event.

In step 714, new control parameters may be produced based on thecalculations of step 712. In step 716, a determination may be made as towhether changes are needed in the current control parameters. Forexample, the calculations of step 712 may result in a decision that thecurrent control parameters are satisfactory (e.g., the event may notaffect the control parameters). If no changes are needed, the method 700returns to step 708. If changes are needed, the on-site controller 144outputs the new parameters in step 718. The method 700 may then returnto step 708. In some embodiments, the determination of step 716 mayoccur before step 714. In such embodiments, step 714 may not be executedif the current control parameters are satisfactory.

In a more detailed example of the method 700, assume that the on-sitecontroller 144 is involved in drilling a borehole and that approximatelysix hundred feet remain to be drilled. An event has been defined thatwarns the on-site controller 144 when the drill bit is predicted toreach a minimum level of efficiency due to wear and this event istriggered in step 710 at the six hundred foot mark. The event may betriggered because the drill bit is within a certain number ofrevolutions before reaching the minimum level of efficiency, within acertain distance remaining (based on strata type, thickness, etc.) thatcan be drilled before reaching the minimum level of efficiency, or maybe based on some other factor or factors. Although the event of thecurrent example is triggered prior to the predicted minimum level ofefficiency being reached in order to proactively schedule drillingchanges if needed, it is understood that the event may be triggered whenthe minimum level is actually reached.

The on-site controller 144 may perform calculations in step 712 thataccount for various factors that may be analyzed to determine how thelast six hundred feet is drilled. These factors may include the rocktype and thickness of the remaining six hundred feet, the predicted wearof the drill bit based on similar drilling conditions, location of thebit (e.g., depth), how long it will take to change the bit, and a costversus time analysis. Generally, faster drilling is more cost effective,but there are many tradeoffs. For example, increasing the WOB ordifferential pressure to increase the rate of penetration may reduce thetime it takes to finish the borehole, but may also wear out the drillbit faster, which will decrease the drilling effectiveness and slow thedrilling down. If this slowdown occurs too early, it may be lessefficient than drilling more slowly. Therefore, there is a tradeoff thatmust be calculated. Too much WOB or differential pressure may also causeother problems, such as damaging downhole tools. Should one of theseproblems occur, taking the time to trip the bit or drill a sidetrack mayresult in more total time to finish the borehole than simply drillingmore slowly, so faster may not be better. The tradeoffs may berelatively complex, with many factors to be considered.

In step 714, the on-site controller 144 produces new control parametersbased on the solution calculated in step 712. In step 716, adetermination is made as to whether the current parameters should bereplaced by the new parameters. For example, the new parameters may becompared to the current parameters. If the two sets of parameters aresubstantially similar (e.g., as calculated based on a percentage changeor margin of error of the current path with a path that would be createdusing the new control parameters) or identical to the currentparameters, no changes would be needed. However, if the new controlparameters call for changes greater than the tolerated percentage changeor outside of the margin of error, they are output in step 718. Forexample, the new control parameters may increase the WOB and alsoinclude the rate of mud flow significantly enough to override theprevious control parameters. In other embodiments, the new controlparameters may be output regardless of any differences, in which casestep 716 may be omitted. In still other embodiments, the current pathand the predicted path may be compared before the new parameters areproduced, in which case step 714 may occur after step 716.

Referring to FIG. 7B and with additional reference to FIG. 7C, a method720 (FIG. 7B) and diagram 740 (FIG. 7C) illustrate a more detailedembodiment of the method 600 of FIG. 6, particularly of step 610. Assteps 722, 724, 726, and 728 are similar or identical to steps 602, 604,606, and 608, respectively, of FIG. 6, they are not described in detailin the present embodiment. In the present example, the action of step610 of FIG. 6 is based on whether the drilling has deviated from theplanned path.

In step 730, a comparison may be made to compare the estimated bitposition and trajectory with a desired point (e.g., a desired bitposition) along the planned path. The estimated bit position may becalculated based on information such as a survey reference point and/orrepresented as an output calculated by a borehole estimator (as will bedescribed later) and may include a bit projection path and/or point thatrepresents a predicted position of the bit if it continues its currenttrajectory from the estimated bit position. Such information may beincluded in the inputs of step 722 and feedback information of step 728or may be obtained in other ways. It is understood that the estimatedbit position and trajectory may not be calculated exactly, but mayrepresent an estimate the current location of the drill bit based on thefeedback information. As illustrated in FIG. 7C, the estimated bitposition is indicated by arrow 743 relative to the desired bit position741 along the planned path 742.

In step 732, a determination may be made as to whether the estimated bitposition 743 is within a defined margin of error of the desired bitposition. If the estimated bit position is within the margin of error,the method 720 returns to step 728. If the estimated bit position is notwithin the margin of error, the on-site controller 144 calculates aconvergence plan in step 734. With reference to FIG. 7C, for purposes ofthe present example, the estimated bit position 743 is outside of themargin of error.

In some embodiments, a projected bit position (not shown) may also beused. For example, the estimated bit position 743 may be extended viacalculations to determine where the bit is projected to be after acertain amount of drilling (e.g., time and/or distance). Thisinformation may be used in several ways. If the estimated bit position743 is outside the margin of error, the projected bit position 743 mayindicate that the current bit path will bring the bit within the marginof error without any action being taken. In such a scenario, action maybe taken only if it will take too long to reach the projected bitposition when a more optimal path is available. If the estimated bitposition is inside the margin of error, the projected bit position maybe used to determine if the current path is directing the bit away fromthe planned path. In other words, the projected bit position may be usedto proactively detect that the bit is off course before the margin oferror is reached. In such a scenario, action may be taken to correct thecurrent path before the margin of error is reached.

The convergence plan identifies a plan by which the bit can be movedfrom the estimated bit position 743 to the planned path 742. It is notedthat the convergence plan may bypass the desired bit position 741entirely, as the objective is to get the actual drilling path back tothe planned path 742 in the most optimal manner. The most optimal mannermay be defined by cost, which may represent a financial value, areliability value, a time value, and/or other values that may be definedfor a convergence path.

As illustrated in FIG. 7C, an infinite number of paths may be selectedto return the bit to the planned path 742. The paths may begin at theestimated bit position 743 or may begin at other points along aprojected path 752 that may be determined by calculating future bitpositions based on the current trajectory of the bit from the estimatedbit position 752. In the present example, a first path 744 results inlocating the bit at a position 745 (e.g., a convergence point). Theconvergence point 745 is outside of a lower limit 753 defined by a mostaggressive possible correction (e.g., a lower limit on a window ofcorrection). This correction represents the most aggressive possibleconvergence path, which may be limited by such factors as a maximumdirectional change possible in the convergence path, where any greaterdirectional change creates a dogleg that makes it difficult orimpossible to run casing or perform other needed tasks. A second path746 results in a convergence point 747, which is right at the lowerlimit 753. A third path 748 results in a convergence point 749, whichrepresents a mid-range convergence point. A third path 750 results in aconvergence point 751, which occurs at an upper limit 754 defined by amaximum convergence delay (e.g., an upper limit on the window ofcorrection).

A fourth path 756 may begin at a projected point or bit position 755that lies along the projected path 752 and result in a convergence point757, which represents a mid-range convergence point. The path 756 may beused by, for example, delaying a trajectory change until the bit reachesthe position 755. Many additional convergence options may be opened upby using projected points for the basis of convergence plans as well asthe estimated bit position.

A fifth path 758 may begin at a projected point or bit position 760 thatlies along the projected path 750 and result in a convergence point 759.In such an embodiment, different convergence paths may include similaror identical path segments, such as the similar or identical path sharedby the convergence points 751 and 759 to the point 760. For example, thepoint 760 may mark a position on the path 750 where a slide segmentbegins (or continues from a previous slide segment) for the path 758 anda straight line path segment begins (or continues) for the path 750. Thesurface steerable system 144 may calculate the paths 750 and 758 as twoentirely separate paths or may calculate one of the paths as deviatingfrom (e.g., being a child of) the other path. Accordingly, any path mayhave multiple paths deviating from that path based on, for example,different slide points and slide times.

Each of these paths 744, 746, 748, 750, 756, and 758 may presentadvantages and disadvantages from a drilling standpoint. For example,one path may be longer and may require more sliding in a relatively softrock layer, while another path may be shorter but may require moresliding through a much harder rock layer. Accordingly, tradeoffs may beevaluated when selecting one of the convergence plans rather than simplyselecting the most direct path for convergence. The tradeoffs may, forexample, consider a balance between ROP, total cost, dogleg severity,and reliability. While the number of convergence plans may vary, theremay be hundreds or thousands of convergence plans in some embodimentsand the tradeoffs may be used to select one of those hundreds orthousands for implementation. The convergence plans from which the finalconvergence plan is selected may include plans calculated from theestimated bit position 743 as well as plans calculated from one or moreprojected points along the projected path.

In some embodiments, straight line projections of the convergence pointvectors, after correction to the well plan 742, may be evaluated topredict the time and/or distance to the next correction requirement.This evaluation may be used when selecting the lowest total cost optionby avoiding multiple corrections where a single more forward thinkingoption might be optimal. As an example, one of the solutions provided bythe convergence planning may result in the most cost effective path toreturn to the well plan 742, but may result in an almost immediate needfor a second correction due to a pending deviation within the well plan.Accordingly, a convergence path that merges the pending deviation withthe correction by selecting a convergence point beyond the pendingdeviation might be selected when considering total well costs.

It is understood that the diagram 740 of FIG. 7C is a two dimensionalrepresentation of a three dimensional environment. Accordingly, theillustrated convergence paths in the diagram 740 of FIG. 7C may be threedimensional. In addition, although the illustrated convergence paths allconverge with the planned path 742, is it understood that someconvergence paths may be calculated that move away from the planned path742 (although such paths may be rejected). Still other convergence pathsmay overshoot the actual path 742 and then converge (e.g., if thereisn't enough room to build the curve otherwise). Accordingly, manydifferent convergence path structures may be calculated.

Referring again to FIG. 7B, in step 736, the on-site controller 144produces revised control parameters based on the convergence plancalculated in step 734. In step 738, the revised control parameters maybe output. It is understood that the revised control parameters may beprovided to get the drill bit back to the planned path 742 and theoriginal control parameters may then be used from that point on(starting at the convergence point). For example, if the convergenceplan selected the path 748, the revised control parameters may be useduntil the bit reaches position 749. Once the bit reaches the position749, the original control parameters may be used for further drilling.Alternatively, the revised control parameters may incorporate theoriginal control parameters starting at the position 749 or mayre-calculate control parameters for the planned path even beyond thepoint 749. Accordingly, the convergence plan may result in controlparameters from the bit position 743 to the position 749, and furthercontrol parameters may be reused or calculated depending on theparticular implementation of the on-site controller 144.

Referring to FIG. 8A, a method 800 illustrates a more detailedembodiment of step 734 of FIG. 7B. It is understood that the convergenceplan of step 734 may be calculated in many different ways, and that 800method provides one possible approach to such a calculation when thegoal is to find the lowest cost solution vector. In the present example,cost may include both the financial cost of a solution and thereliability cost of a solution. Other costs, such as time costs, mayalso be included. For purposes of example, the diagram 740 of FIG. 7C isused.

In step 802, multiple solution vectors are calculated from the currentposition 743 to the planned path 742. These solution vectors may includethe paths 744, 746, 748, and 750. Additional paths (not shown in FIG.7C) may also be calculated. The number of solution vectors that arecalculated may vary depending on various factors. For example, thedistance available to build a needed curve to get back to the plannedpath 742 may vary depending on the current bit location and orientationrelative to the planned path. A greater number of solution vectors maybe available when there is a greater distance in which to build a curvethan for a smaller distance since the smaller distance may require amuch more aggressive build rate that excludes lesser build rates thatmay be used for the greater distance. In other words, the earlier anerror is caught, the more possible solution vectors there will generallybe due to the greater distance over which the error can be corrected.While the number of solution vectors that are calculated in this stepmay vary, there may be hundreds or thousands of solution vectorscalculated in some embodiments.

In step 804, any solution vectors that fall outside of defined limitsare rejected, such as solution vectors that fall outside the lower limit753 and the upper limit 754. For example, the path 744 would be rejectedbecause the convergence point 745 falls outside of the lower limit 753.It is understood that the path 744 may be rejected for an engineeringreason (e.g., the path would require a dogleg of greater than allowedseverity) prior to cost considerations, or the engineering reason may beconsidered a cost.

In step 806, a cost is calculated for each remaining solution vector. Asillustrated in FIG. 7C, the costs may be represented as a cost matrix(that may or may not be weighted) with each solution vector havingcorresponding costs in the cost matrix. In step 808, a minimum of thesolution vectors may be taken to identify the lowest cost solutionvector. It is understood that the minimum cost is one way of selectingthe desired solution vector, and that other ways may be used.Accordingly, step 808 is concerned with selecting an optimal solutionvector based on a set of target parameters, which may include one ormore of a financial cost, a time cost, a reliability cost, and/or anyother factors, such as an engineering cost like dogleg severity, thatmay be used to narrow the set of solution vectors to the optimalsolution vector.

By weighting the costs, the cost matrix can be customized to handle manydifferent cost scenarios and desired results. For example, if time is ofprimary importance, a time cost may be weighted over financial andreliability costs to ensure that a solution vector that is faster willbe selected over other solution vectors that are substantially the samebut somewhat slower, even though the other solution vectors may be morebeneficial in terms of financial cost and reliability cost. In someembodiments, step 804 may be combined with step 808 and solution vectorsfalling outside of the limits may be given a cost that ensures they willnot be selected. In step 810, the solution vector corresponding to theminimum cost is selected.

Referring to FIG. 8B, a method 820 illustrates one embodiment of anevent-based process that may be executed by the on-site controller 144of FIG. 2A. It is understood that an event may represent many differentscenarios in the surface steerable system 201. In the present example,in step 822, an event may occur that indicates that a prediction is notcorrect based on what has actually occurred. For example, a formationlayer is not where it is expected (e.g., too high or low), a selectedbit did not drill as expected, or a selected mud motor did not buildcurve as expected. The prediction error may be identified by comparingexpected results with actual results or by using other detectionmethods.

In step 824, a reason for the error may be determined as the surfacesteerable system 201 and its data may provide an environment in whichthe prediction error can be evaluated. For example, if a bit did notdrill as expected, the method 820 may examine many different factors,such as whether the rock formation was different than expected, whetherthe drilling parameters were correct, whether the drilling parameterswere correctly entered by the driller, whether another error and/orfailure occurred that caused the bit to drill poorly, and whether thebit simply failed to perform. By accessing and analyzing the availabledata, the reason for the failure may be determined.

In step 826, a solution may be determined for the error. For example, ifthe rock formation was different than expected, the database 128 may beupdated with the correct rock information and new drilling parametersmay be obtained for the drilling rig 110. Alternatively, the current bitmay be tripped and replaced with another bit more suitable for the rock.In step 828, the current drilling predictions (e.g., well plan, buildrate, slide estimates) may be updated based on the solution and thesolution may be stored in the database 128 for use in futurepredictions. Accordingly, the method 820 may result in benefits forfuture wells as well as improving current well predictions.

Referring to FIG. 8C, a method 830 illustrates one embodiment of anevent-based process that may be executed by the on-site controller 144of FIG. 2A. The method 830 is directed to recalibration forecasting thatmay be triggered by an event, such as an event detected in step 610 ofFIG. 6. It is understood that the recalibration described in thisembodiment may not be the same as calculating a convergence plan,although calculating a convergence plan may be part of therecalibration. As an example of a recalibration triggering event, ashift in ROP and/or GAMMA readings may indicate that a formation layer(e.g., the layer 170A of FIG. 1B) is actually twenty feet higher thanplanned. This will likely impact the well plan, as build ratepredictions and other drilling parameters may need to be changed.Accordingly, in step 832, this event is identified.

In step 834, a forecast may be made as to the impact of the event. Forexample, the surface steerable system 201 may determine whether theprojected build rate needed to land the curve can be met based on thetwenty foot difference. This determination may include examining thecurrent location of the bit, the projected path, and similarinformation.

In step 836, modifications may be made based on the forecast. Forexample, if the projected build rate can be met, then modifications maybe made to the drilling parameters to address the formation depthdifference, but the modifications may be relatively minor. However, ifthe projected build rate cannot be met, the surface steerable system 201may determine how to address the situation by, for example, planning abit trip to replace the current BHA with a BHA capable of making a newand more aggressive curve.

Such decisions may be automated or may require input or approval by thedrilling engineer 302, geologist 304, or other individuals. For example,depending on the distance to the kick off point, the surface steerablesystem 201 may first stop drilling and then send an alert to anauthorized individual, such as the drilling engineer 302 and/orgeologist 304. The drilling engineer 302 and geologist 304 may thenbecome involved in planning a solution or may approve of a solutionproposed by the surface steerable system 201. In some embodiments, thesurface steerable system 201 may automatically implement its calculatedsolution. Parameters may be set for such automatic implementationmeasures to ensure that drastic deviations from the original well plando not occur automatically while allowing the automatic implementationof more minor measures.

It is understood that such recalibration forecasts may be performedbased on many different factors and may be triggered by many differentevents. The forecasting portion of the process is directed toanticipating what changes may be needed due to the recalibration andcalculating how such changes may be implemented. Such forecastingprovides cost advantages because more options may be available when aproblem is detected earlier rather than later. Using the previousexample, the earlier the difference in the depth of the layer isidentified, the more likely it is that the build rate can be met withoutchanging the BHA.

Referring to FIG. 8D, a method 840 illustrates one embodiment of anevent-based process that may be executed by the on-site controller 144of FIG. 2A. The method 840 is directed to self-tuning that may beperformed by the on-site controller 144 based on factors such as ROP,total cost, and reliability. By self-tuning, the on-site controller 144may execute a learning process that enables it to optimize the drillingperformance of the drilling rig 110. Furthermore, the self-tuningprocess enables a balance to be reached that provides reliability whilealso lowering costs. Reliability in drilling operations is often tied tovibration and the problems that vibration can cause, such as stick-slipand whirling. Such vibration issues can damage or destroy equipment andcan also result in a very uneven surface in the borehole that can causeother problems such as friction loading of future drilling operations aspipe/casing passes through that area of the borehole. Accordingly, it isdesirable to minimize vibration while optimizing performance, sinceover-correcting for vibration may result in slower drilling thannecessary. It is understood that the present optimization may involve achange in any drilling parameter and is not limited to a particularpiece of equipment or control system. In other words, parameters acrossthe entire drilling rig 110 and BHA may be changed during theself-tuning process. Furthermore, the optimization process may beapplied to production by optimizing well smoothness and other factorsaffecting production. For example, by minimizing dogleg severity,production may be increased for the lifetime of the well.

Accordingly, in step 842, one or more target parameters are identified.For example, the target parameter may be an MSE of 50 ksi or an ROP of100 ft/hr that the on-site controller 144 is to establish and maintain.In step 844, a plurality of control parameters are identified for usewith the drilling operation. The control parameters are selected to meetthe target MSE of 50 ksi or ROP of 100 ft/hr. The drilling operation isstarted with the control parameters, which may be used until the targetMSE or ROP is reached. In step 846, feedback information is receivedfrom the drilling operation when the control parameters are being used,so the feedback represents the performance of the drilling operation ascontrolled by the control parameters. Historical information may also beused in step 846. In step 848, an operational baseline is establishedbased on the feedback information.

In step 850, at least one of the control parameters is changed to modifythe drilling operation, although the target MSE or ROP should bemaintained. For example, some or all of the control parameters may beassociated with a range of values and the value of one or more of thecontrol parameters may be changed. In step 852, more feedbackinformation is received, but this time the feedback reflects theperformance of the drilling operation with the changed controlparameter. In step 854, a performance impact of the change is determinedwith respect to the operational baseline. The performance impact mayoccur in various ways, such as a change in MSE or ROP and/or a change invibration. In step 856, a determination is made as to whether thecontrol parameters are optimized. If the control parameters are notoptimized, the method 840 returns to step 850. If the control parametersare optimized, the method 840 moves to step 858. In step 858, theoptimized control parameters are used for the current drilling operationwith the target MSE or ROP and stored (e.g., in the database 128) foruse in later drilling operations and operational analyses. This mayinclude linking formation information to the control parameters in theregional database 128.

Referring to FIG. 9, one embodiment of a system architecture 900 isillustrated that may be used for the on-site controller 144 of FIG. 1A.The system architecture 900 includes interfaces configured to interactwith external components and internal modules configured to processinformation. The interfaces may include an input driver 902, a remotesynchronization interface 904, and an output interface 918, which mayinclude at least one of a graphical user interface (GUI) 906 and anoutput driver 908. The internal modules may include a database query andupdate engine/diagnostic logger 910, a local database 912 (which may besimilar or identical to the database 410 of FIG. 4), a guidance controlloop (GCL) module 914, and an autonomous control loop (ACL) module 916.It is understood that the system architecture 900 is merely one exampleof a system architecture that may be used for the on-site controller 144and the functionality may be provided for the on-site controller 144using many different architectures. Accordingly, the functionalitydescribed herein with respect to particular modules and architecturecomponents may be combined, further separated, and organized in manydifferent ways.

It is understood that the computer steerable system 144 may performcertain computations to prevent errors or inaccuracies from accumulatingand throwing off calculations. For example, as will be described later,the input driver 902 may receive Wellsite Information TransferSpecification (WITS) input representing absolute pressure, while thesurface steerable system 144 needs differential pressure and needs anaccurate zero point for the differential pressure. Generally, thedriller will zero out the differential pressure when the drillstring ispositioned with the bit off bottom and full pump flow is occurring.However, this may be a relatively sporadic event. Accordingly, thesurface steerable system 144 may recognize when the bit is off bottomand target flow rate has been achieved and zero out the differentialpressure.

Another computation may involve block height, which needs to becalibrated properly. For example, block height may oscillate over a widerange, including distances that may not even be possible for aparticular drilling rig. Accordingly, if the reported range is sixtyfeet to one hundred and fifty feet and there should only be one hundredfeet, the surface steerable system 144 may assign a zero value to thereported sixty feet and a one hundred foot value to the reported onehundred and fifty feet. Furthermore, during drilling, error graduallyaccumulates as the cable is shifted and other events occur. The surfacesteerable system 144 may compute its own block height to predict whenthe next connection occurs and other related events, and may also takeinto account any error that may be introduced by cable issues.

Referring specifically to FIG. 9, the input driver 902 provides outputto the GUI 906, the database query and update engine/diagnostic logger910, the GCL 914, and the ACL 916. The input driver 902 is configured toreceive input for the on-site controller 144. It is understood that theinput driver 902 may include the functionality needed to receive variousfile types, formats, and data streams. The input driver 902 may also beconfigured to convert formats if needed. Accordingly, the input driver902 may be configured to provide flexibility to the on-site controller144 by handling incoming data without the need to change the internalmodules. In some embodiments, for purposes of abstraction, the protocolof the data stream can be arbitrary with an input event defined as asingle change (e.g., a real time sensor change) of any of the giveninputs.

The input driver 902 may receive various types of input, including rigsensor input (e.g., from the sensor system 214 of FIG. 2A), well plandata, and control data (e.g., engineering control parameters). Forexample, rig sensor input may include hole depth, bit depth, toolface,inclination, azimuth, true vertical depth, gamma count, standpipepressure, mud flow rate, rotary RPMs, bit speed, ROP, and WOB. The wellplan data may include information such as projected starting and endinglocations of various geologic layers at vertical depth points along thewell plan path, and a planned path of the borehole presented in a threedimensional space. The control data may be used to define maximumoperating parameters and other limitations to control drilling speed,limit the amount of deviation permitted from the planned path, definelevels of authority (e.g., can an on-site operator make a particulardecision or should it be made by an off-site engineer), and similarlimitations. The input driver 902 may also handle manual input, such asinput entered via a keyboard, a mouse, or a touch screen. In someembodiments, the input driver 902 may also handle wireless signal input,such as from a cell phone, a smart phone, a PDA, a tablet, a laptop, orany other device capable of wirelessly communicating with the on-sitecontroller 144 through a network locally and/or offsite.

The database query and update engine/diagnostic logger 910 receivesinput from the input driver 902, the GCL 914, and ACL 916, and providesoutput to the local database 912 and GUI 906. The database query andupdate engine/diagnostic logger 910 is configured to manage thearchiving of data to the local database 912. The database query andupdate engine/diagnostic logger 910 may also manage some functionalrequirements of a remote synchronization server (RSS) via the remotesynchronization interface 904 for archiving data that will be uploadedand synchronized with a remote database, such as the database 128 ofFIG. 1A. The database query and update engine/diagnostic logger 910 mayalso be configured to serve as a diagnostic tool for evaluatingalgorithm behavior and performance against raw rig data and sensorfeedback data.

The local database 912 receives input from the database query and updateengine/diagnostic logger 910 and the remote synchronization interface904, and provides output to the GCL 914, the ACL 916, and the remotesynchronization interface 904. It is understood that the local database912 may be configured in many different ways. As described in previousembodiments, the local database 912 may store both current and historicinformation representing both the current drilling operation with whichthe on-site controller 144 is engaged as well as regional informationfrom the database 128.

The GCL 914 receives input from the input driver 902 and the localdatabase 912, and provides output to the database query and updateengine/diagnostic logger 910, the GUI 906, and the ACL 916. Although notshown, in some embodiments, the GCL 906 may provide output to the outputdriver 908, which enables the GCL 914 to directly control third partysystems and/or interface with the drilling rig alone or with the ACL916. An embodiment of the GCL 914 is discussed below with respect toFIG. 11.

The ACL 916 receives input from the input driver 902, the local database912, and the GCL 914, and provides output to the database query andupdate engine/diagnostic logger 910 and output driver 908. An embodimentof the ACL 916 is discussed below with respect to FIG. 12.

The output interface 918 receives input from the input driver 902, theGCL 914, and the ACL 916. In the present example, the GUI 906 receivesinput from the input driver 902 and the GCL 914. The GUI 906 may displayoutput on a monitor or other visual indicator. The output driver 908receives input from the ACL 916 and is configured to provide aninterface between the on-site controller 144 and external controlsystems, such as the control systems 208, 210, and 212 of FIG. 2A.

It is understood that the system architecture 900 of FIG. 9 may beconfigured in many different ways. For example, various interfaces andmodules may be combined or further separated. Accordingly, the systemarchitecture 900 provides one example of how functionality may bestructured to provide the on-site controller 144, but the on-sitecontroller 144 is not limited to the illustrated structure of FIG. 9.

Referring to FIG. 10, one embodiment of the input driver 902 of thesystem architecture 900 of FIG. 9 is illustrated in greater detail. Inthe present example, the input driver 902 may be configured to receiveinput via different input interfaces, such as a serial input driver 1002and a Transmission Control Protocol (TCP) driver 1004. Both the serialinput driver 1002 and the TCP input driver 1004 may feed into a parser1006.

The parser 1006 in the present example may be configured in accordancewith a specification such as WITS and/or using a standard such asWellsite Information Transfer Standard Markup Language (WITSML). WITS isa specification for the transfer of drilling rig-related data and uses abinary file format. WITS may be replaced or supplemented in someembodiments by WITSML, which relies on eXtensible Markup Language (XML)for transferring such information. The parser 1006 may feed into thedatabase query and update engine/diagnostic logger 910, and also to theGCL 914 and GUI 906 as illustrated by the example parameters of block1010. The input driver 902 may also include a non-WITS input driver 1008that provides input to the ACL 916 as illustrated by block 1012.

Referring to FIG. 11, one embodiment of the GCL 914 of FIG. 9 isillustrated in greater detail. In the present example, the GCL 914 mayinclude various functional modules, including a build rate predictor1102, a geo modified well planner 1104, a borehole estimator 1106, aslide estimator 1108, an error vector calculator 1110, a geologicaldrift estimator 1112, a slide planner 1114, a convergence planner 1116,and a tactical solution planner 1118. In the following description ofthe GCL 914, the term external input refers to input received fromoutside the GCL 914 (e.g., from the input driver 902 of FIG. 9), whileinternal input refers to input received by a GCL module from another GCLmodule.

The build rate predictor 1102 receives external input representing BHAand geological information, receives internal input from the boreholeestimator 1106, and provides output to the geo modified well planner1104, slide estimator 1108, slide planner 1114, and convergence planner1116. The build rate predictor 1102 is configured to use the BHA andgeological information to predict the drilling build rates of currentand future sections of a well. For example, the build rate predictor1102 may determine how aggressively the curve will be built for a givenformation with given BHA and other equipment parameters.

The build rate predictor 1102 may use the orientation of the BHA to theformation to determine an angle of attack for formation transitions andbuild rates within a single layer of a formation. For example, if thereis a layer of rock with a layer of sand above it, there is a formationtransition from the sand layer to the rock layer. Approaching the rocklayer at a ninety degree angle may provide a good face and a clean drillentry, while approaching the rock layer at a forty-five degree angle maybuild a curve relatively quickly. An angle of approach that is nearparallel may cause the bit to skip off the upper surface of the rocklayer. Accordingly, the build rate predictor 1102 may calculate BHAorientation to account for formation transitions. Within a single layer,the build rate predictor 1102 may use BHA orientation to account forinternal layer characteristics (e.g., grain) to determine build ratesfor different parts of a layer.

The BHA information may include bit characteristics, mud motor bendsetting, stabilization and mud motor bit to bend distance. Thegeological information may include formation data such as compressivestrength, thicknesses, and depths for formations encountered in thespecific drilling location. Such information enables a calculation-basedprediction of the build rates and ROP that may be compared to both realtime results (e.g., obtained while drilling the well) and regionalhistorical results (e.g., from the database 128) to improve the accuracyof predictions as the drilling progresses. Future formation build ratepredictions may be used to plan convergence adjustments and confirm thattargets can be achieved with current variables in advance.

The geo modified well planner 1104 receives external input representinga well plan, internal input from the build rate predictor 1102 and thegeo drift estimator 1112, and provides output to the slide planner 1114and the error vector calculator 1110. The geo modified well planner 1104uses the input to determine whether there is a more optimal path thanthat provided by the external well plan while staying within theoriginal well plan error limits. More specifically, the geo modifiedwell planner 1104 takes geological information (e.g., drift) andcalculates whether another solution to the target may be more efficientin terms of cost and/or reliability. The outputs of the geo modifiedwell planner 1104 to the slide planner 1114 and the error vectorcalculator 1110 may be used to calculate an error vector based on thecurrent vector to the newly calculated path and to modify slidepredictions.

In some embodiments, the geo modified well planner 1104 (or anothermodule) may provide functionality needed to track a formation trend. Forexample, in horizontal wells, the geologist 304 may provide the surfacesteerable system 144 with a target inclination that the surfacesteerable system 144 is to attempt to hold. For example, the geologist304 may provide a target to the directional driller 306 of 90.5-91degrees of inclination for a section of the well. The geologist 304 mayenter this information into the surface steerable system 144 and thedirectional driller 306 may retrieve the information from the surfacesteerable system 144. The geo modified well planner 1104 may then treatthe target as a vector target, for example, either by processing theinformation provided by the geologist 304 to create the vector target orby using a vector target entered by the geologist 304. The geo modifiedwell planner 1104 may accomplish this while remaining within the errorlimits of the original well plan.

In some embodiments, the geo modified well planner 1104 may be anoptional module that is not used unless the well plan is to be modified.For example, if the well plan is marked in the surface steerable system201 as non-modifiable, the geo modified well planner 1104 may bebypassed altogether or the geo modified well planner 1104 may beconfigured to pass the well plan through without any changes.

The borehole estimator 1106 receives external inputs representing BHAinformation, measured depth information, survey information (e.g.,azimuth and inclination), and provides outputs to the build ratepredictor 1102, the error vector calculator 1110, and the convergenceplanner 1116. The borehole estimator 1106 is configured to provide areal time or near real time estimate of the actual borehole and drillbit position and trajectory angle. This estimate may use both straightline projections and projections that incorporate sliding. The boreholeestimator 1106 may be used to compensate for the fact that a sensor isusually physically located some distance behind the bit (e.g., fiftyfeet), which makes sensor readings lag the actual bit location by fiftyfeet. The borehole estimator 1106 may also be used to compensate for thefact that sensor measurements may not be continuous (e.g., a sensormeasurement may occur every one hundred feet).

The borehole estimator 1106 may use two techniques to accomplish this.First, the borehole estimator 1106 may provide the most accurateestimate from the surface to the last survey location based on thecollection of all survey measurements. Second, the borehole estimator1106 may take the slide estimate from the slide estimator 1108(described below) and extend this estimation from the last survey pointto the real time drill bit location. Using the combination of these twoestimates, the borehole estimator 1106 may provide the on-sitecontroller 144 with an estimate of the drill bit's location andtrajectory angle from which guidance and steering solutions can bederived. An additional metric that can be derived from the boreholeestimate is the effective build rate that is achieved throughout thedrilling process. For example, the borehole estimator 1106 may calculatethe current bit position and trajectory 743 in FIG. 7C.

The slide estimator 1108 receives external inputs representing measureddepth and differential pressure information, receives internal inputfrom the build rate predictor 1102, and provides output to the boreholeestimator 1106 and the geo modified well planner 1104. The slideestimator 1108, which may operate in real time or near real time, isconfigured to sample toolface orientation, differential pressure,measured depth (MD) incremental movement, MSE, and other sensor feedbackto quantify/estimate a deviation vector and progress while sliding.

Traditionally, deviation from the slide would be predicted by a humanoperator based on experience. The operator would, for example, use along slide cycle to assess what likely was accomplished during the lastslide. However, the results are generally not confirmed until the MWDsurvey sensor point passes the slide portion of the borehole, oftenresulting in a response lag defined by the distance of the sensor pointfrom the drill bit tip (e.g., approximately fifty feet). This lagintroduces inefficiencies in the slide cycles due to over/undercorrection of the actual path relative to the planned path.

With the slide estimator 1108, each toolface update is algorithmicallymerged with the average differential pressure of the period between theprevious and current toolfaces, as well as the MD change during thisperiod to predict the direction, angular deviation, and MD progressduring that period. As an example, the periodic rate may be between tenand sixty seconds per cycle depending on the tool face update rate ofthe MWD tool. With a more accurate estimation of the slideeffectiveness, the sliding efficiency can be improved. The output of theslide estimator 1108 is periodically provided to the borehole estimator1106 for accumulation of well deviation information, as well to the geomodified well planner 1104. Some or all of the output of the slideestimator 1108 may be output via a display such as the display 250 ofFIG. 2B.

The error vector calculator 1110 receives internal input from the geomodified well planner 1104 and the borehole estimator 1106. The errorvector calculator 1110 is configured to compare the planned well path tothe actual borehole path and drill bit position estimate. The errorvector calculator 1110 may provide the metrics used to determine theerror (e.g., how far off) the current drill bit position and trajectoryare from the plan. For example, the error vector calculator 1110 maycalculate the error between the current position 743 of FIG. 7C to theplanned path 742 and the desired bit position 741. The error vectorcalculator 1110 may also calculate a projected bit position/projectedpath representing the future result of a current error as describedpreviously with respect to FIG. 7B.

The geological drift estimator 1112 receives external input representinggeological information and provides outputs to the geo modified wellplanner 1104, slide planner 1114, and tactical solution planner 1118.During drilling, drift may occur as the particular characteristics ofthe formation affect the drilling direction. More specifically, theremay be a trajectory bias that is contributed by the formation as afunction of drilling rate and BHA. The geological drift estimator 1112is configured to provide a drift estimate as a vector. This vector canthen be used to calculate drift compensation parameters that can be usedto offset the drift in a control solution.

The drift vector information may also be used in determinationsinvolving creation of a convergence path wherein the drift vector effecton drilling direction may be utilized in determining a drillingdirection in order that a direction of drilling may be utilized in orderto take into account the drift vector provided by the present formationcharacteristic and drill bit characteristics as will be more fullydescribed hereinbelow.

The slide planner 1114 receives internal input from the build ratepredictor 1102, the geo modified well planner 1104, the error vectorcalculator 1110, and the geological drift estimator 1112, and providesoutput to the convergence planner 1116 as well as an estimated time tothe next slide. The slide planner 1114 is configured to evaluate aslide/drill ahead cost equation and plan for sliding activity, which mayinclude factoring in BHA wear, expected build rates of current andexpected formations, and the well plan path. During drill ahead, theslide planner 1114 may attempt to forecast an estimated time of the nextslide to aid with planning. For example, if additional lubricants (e.g.,beads) are needed for the next slide and pumping the lubricants into thedrill string needs to begin thirty minutes before the slide, theestimated time of the next slide may be calculated and then used toschedule when to start pumping the lubricants.

Functionality for a loss circulation material (LCM) planner may beprovided as part of the slide planner 1114 or elsewhere (e.g., as astand-alone module or as part of another module described herein). TheLCM planner functionality may be configured to determine whetheradditives need to be pumped into the borehole based on indications suchas flow-in versus flow-back measurements. For example, if drillingthrough a porous rock formation, fluid being pumped into the boreholemay get lost in the rock formation. To address this issue, the LCMplanner may control pumping LCM into the borehole to clog up the holesin the porous rock surrounding the borehole to establish a moreclosed-loop control system for the fluid.

The slide planner 1114 may also look at the current position relative tothe next connection. A connection may happen every ninety to one hundredfeet (or some other distance or distance range based on the particularsof the drilling operation) and the slide planner 1114 may avoid planninga slide when close to a connection and/or when the slide would carrythrough the connection. For example, if the slide planner 1114 isplanning a fifty foot slide but only twenty feet remain until the nextconnection, the slide planner 1114 may calculate the slide startingafter the next connection and make any changes to the slide parametersthat may be needed to accommodate waiting to slide until after the nextconnection. This avoids inefficiencies that may be caused by startingthe slide, stopping for the connection, and then having to reorient thetoolface before finishing the slide. During slides, the slide planner1114 may provide some feedback as to the progress of achieving thedesired goal of the current slide.

In some embodiments, the slide planner 1114 may account for reactivetorque in the drillstring. More specifically, when rotating isoccurring, there is a reactional torque wind up in the drillstring. Whenthe rotating is stopped, the drillstring unwinds, which changes toolfaceorientation and other parameters. When rotating is started again, thedrillstring starts to wind back up. The slide planner 1114 may accountfor this reactional torque so that toolface references are maintainedrather than stopping rotation and then trying to adjust to an optimaltool face orientation. While not all MWD tools may provide toolfaceorientation when rotating, using one that does supply such informationfor the GCL 914 may significantly reduce the transition time fromrotating to sliding.

In additional embodiments, the slide planner 1114 may also use driftinformation provided from the geo drift estimator 1112 in order toperform tool face targeting calculations in order to plan a drillingsegment from a present bit location to a target bit location at alocation that attempts to bring the bit more in line with apredetermined drilling target path.

Referring now also to FIG. 26, there is more particularly illustratedthe slide planner 1114 and the components associated with determining aconvergence path that takes into account drift information provided bythe drift estimator 1112. Initially, a look ahead estimator 2602utilizes information provided by the system on the system build rate, anerror vector associated with error vector calculations from the errorvector calculator 110 indicating the degree of error from a target wellpath and a present well plan provided by the well planner 1104. The wellplan provides information with respect to the desired target path wherethe bottom hole assembly should presently be located. The error vectorprovides information with respect to the error from the indicated wellpath, and the build rate demonstrates the predicted build rate that hasbeen determined thus far within the drilling. Each of these pieces ofinformation are provided to the look ahead estimator 2602 thatdetermines a look ahead point that is a fixed distance ahead of thebottom hole assembly for getting the bottom hole assembly back on targetwith respect to the well plan. The look ahead estimator 2602 calculatesa direction of drilling toward the look ahead point by establishing atool face vector for the bottom hole assembly. The tool face vectorcomprises a vector toward the look ahead point transposed onto a planethat is perpendicular to the bottom hole assembly. The toolface vectorshows the orientation of the toolface while sliding to help achieveconvergence with the target well path as the bottom hole assembly drillstoward moving look ahead point that is a fixed distance ahead of thebottom hole assembly. The calculated tool face vector is provided to adrift compensator 2604 which additionally receives the drift estimateinformation form the drift estimator 1112. The drift compensator 2604determines a new adjusted toolface vector that adjusts the toolfacevector based upon the drift associated with the present geologicalformation that the bottom hole assembly is passing through in an attemptto bring the bottom hole assembly back into convergence with the targetwell path as the bottom hole assembly travel toward its moving lookahead point that is a fixed distance ahead of the bottom hole assembly.The adjustment to the tool face vector direction takes into account thegeological formation drift that has been calculated from recent drillingoperations.

Referring now also to FIG. 27A there is more particularly illustratedthe drilling path associated with this process. Dashed line 2702illustrates the target drill path that the bottom hole assembly isattempting to drill along according to a created well plan. Line 2704 upto point 2706 illustrates the actual drill path that has been achievedup to a selected point in time. As can be seen, the point 2706 is notlocated upon the desired target path 2702. Using the look aheadestimator 2602, a toolface vector is determined from the currentposition 2706 to cause the bottom hole assembly to converge toward thetarget drill path 2702 as the bottom hole assembly moves from thepresent toolface location 2706 toward the moving look ahead point 2708that remains a fixed distance 2710 out from the front of the bottom holeassembly. The drilling path back toward convergence with the target path2702 consists of a series of slides 2712 represented by curved portionsof the drill path and rotations 2714 represented by the straightportions of the drill path that take the bit back toward convergencewith the target path 2702. However, the slides 2712 of the drill path2710 does not take into account the geological drift associated with thegeological formation that the bottom hole assembly is drilling through.In actual operation, the drift associated with the drilling operationwill affect the drill path location such that attempting to drill alonga toolface vector that attempts to create path 2710 will cause thebottom hole assembly to actually follow a path above or below thedesired drilling path that either overshoots or undershoots that targetdrill path 2702.

In order to compensate for this, the drift compensator 2604 will alterthe toolface vector to take into account the geological drift occurringwhen drilling over the rotation portions of the drilling path. Referringnow to FIG. 27B, slide 2716 and rotation 2718 represent an idealslide/rotation drilling sequence that is not affected by geologicaldrift. In this case the bit would move from an initial point 2722 to anending point 2724 as expected. In the case of drift that drift isforcing the bit to move downward as illustrated generally at 2726, theslide 2728 will appear to point the bit above the desired endpoint 2724after the rotation portion 2730. However the downward drift 2726 willforce the bit in a downward direction such that the bit will end up atpoint 2724. This type of toolface vector would be utilized when thegeological drift tendency would be to drive the bottom hole assemblybelow the planned drill path 2702.

In a similar manner, when the drift is forcing the bit to move upward asillustrated generally at 2732, the slide 2734 will appear to point thebit above the desired endpoint 2724 after the rotation portion 2730.However the upward drift 2726 will force the bit in an upward directionsuch that the bit will end up at point 2724 after the slide 2734 androtation 2730. This type of toolface vector would be utilized when thegeological drift tendency would be to drive the bottom hole assemblyabove the planned drill path 2702. Thus, the drift adjusted toolfacevectors for providing slides 2728 or 2734 compensate for the naturaldrift tendency of the geological formation during the rotation portionsof drilling to arrive at a desired target location.

While the present description with respect to FIG. 27 has been made withrespect to establishing a toolface vector to create a path above orbelow a target path 2702 in the Y axis, the drift associated with adrilling bit may occur in three dimensions. Thus, the drift adjustedtoolface vector may be established anywhere in three dimensions in orderto ultimately achieve a convergence with the desired target path 2702while taking into account any number of drift forces acting on the bit.

For example, assume the drilling operator is looking a distance of 100feet ahead of the present drill point location on the well plan. If therecent historical drift information is causing the drill bit to drift up2 degrees per 100 feet, the toolface vector would use an average angleover the 100 foot window to determine a net 1.8 foot upward migration toachieve intersection with the target path at the desired location. Tocompensate a toolface vector down from the well plan by 1.8 feet at adistance of 100 feet ahead of the current position would be utilized forthe look ahead reference target point.

Referring now to FIG. 27C, rather than calculating a single toolfacevector or group of toolface vectors to determine a convergence path fromthe present bit location 2706 to a target drill path, the driftcompensator 2604 may determine a number of potential toolface vectorsassociated with different slides 2740 and rotations 2742 to provide aplurality of drill paths 2744 to enable a system to further base targetconvergence decisions on cost of drilling paths that utilized multipledrilling paths. Thus, multiple toolface vectors may be determined foreach slide point creating multiple paths accounting for drift, and amost cost effective path selected. In some cases, the most directdrilling path may not be the most cost effective one and variations fromthe most direct toolface vector may be utilized in order to carry outvarious cost concerns.

In addition to determining a sweep of toolface vectors for determining amost cost effective drilling path, a sweep of toolface vectors may beselected for addressing total vertical depth (TVD) errors and todetermining more aggressive convergence paths for the BHA to the targetdrill path. In this manner various ways for correcting TVD errors ormore quickly seeking a convergence path may be presented and selectedbased upon differing drilling needs.

Referring now to FIG. 28, there is more particularly illustrated a flowchart describing the process of FIGS. 26 and 27. Initially, at step2802, a present position of the drilling tool is determined during aslide. A toolface vector necessary to converge with a desired targetpath at a look ahead point a fixed distance ahead of the bit iscalculated at step 2804 utilizing information such as the build rate,present error vector and well plan information within the look aheadestimator 2602. The desired toolface vector is further combined withgeologic formation drift estimate information within the drift estimator2604 to move the look ahead point and determine the compensated toolfacevector at step 2806. The bottom hole assembly is oriented during slidingin accordance with the compensated toolface vector and then through arotation at steps 2808 and 2810 providing a path that achieves thedesired convergence. Inquiry step 2812 determines if the desiredconvergence with the target path has been achieved. If not controlpasses back to step 2802. If a desired convergence has been achieved,the processed is determined to complete at step 2814.

Thus, the above-described feature operates in a similar fashion to thatof a sharp shooter when adjusting their scope to account for theirmovement in a bullet over a long target distance. The sharp shooter mustaccount for bullet drop occurring due to gravity and side to sidecompensation due to a cross-wind. The toolface vector is adjusted in asimilar manner to have the bottom hole assembly converge with the targetdrill path utilizing the recent drift information associated with thebottom hole assembly

While a foregoing discussion has been done with respect to the driftforces applied to a bottom hole assembly as it is drilling through adrilling formation, the same concepts may be applied to any forcesacting upon the bottom hole assembly to cause the bottomhole assembly tomove indirectly from a first point toward a second point when thedrilling rig is driving the bit from a first point toward a secondpoint.

The convergence planner 1116 receives internal inputs from the buildrate predictor 1102, the borehole estimator 1106, and the slide planner1114, and provides output to the tactical solution planner 1118. Theconvergence planner 1116 is configured to provide a convergence planwhen the current drill bit position is not within a defined margin oferror of the planned well path. The convergence plan represents a pathfrom the current drill bit position to an achievable and optimalconvergence target point along the planned path. The convergence planmay take account the amount of sliding/drilling ahead that has beenplanned to take place by the slide planner 1114. The convergence planner1116 may also use BHA orientation information for angle of attackcalculations when determining convergence plans as described above withrespect to the build rate predictor 1102. The solution provided by theconvergence planner 1116 defines a new trajectory solution for thecurrent position of the drill bit. The solution may be real time, nearreal time, or future (e.g., planned for implementation at a futuretime). For example, the convergence planner 1116 may calculate aconvergence plan as described previously with respect to FIGS. 7C and 8.

The tactical solution planner 1118 receives internal inputs from thegeological drift estimator 1112 and the convergence planner 1116, andprovides external outputs representing information such as toolfaceorientation, differential pressure, and mud flow rate. The tacticalsolution planner 1118 is configured to take the trajectory solutionprovided by the convergence planner 1116 and translate the solution intocontrol parameters that can be used to control the drilling rig 110. Forexample, the tactical solution planner 1118 may take the solution andconvert the solution into settings for the control systems 208, 210, and212 to accomplish the actual drilling based on the solution. Thetactical solution planner 1118 may also perform performance optimizationas described previously. The performance optimization may apply tooptimizing the overall drilling operation as well as optimizing thedrilling itself (e.g., how to drill faster).

Other functionality may be provided by the GCL 914 in additional modulesor added to an existing module. For example, there is a relationshipbetween the rotational position of the drill pipe on the surface and theorientation of the downhole toolface. Accordingly, the GCL 914 mayreceive information corresponding to the rotational position of thedrill pipe on the surface. The GCL 914 may use this surface positionalinformation to calculate current and desired toolface orientations.These calculations may then be used to define control parameters foradjusting the top drive or Kelly drive to accomplish adjustments to thedownhole toolface in order to steer the well.

For purposes of example, an object-oriented software approach may beutilized to provide a class-based structure that may be used with theGCL 914 and/or other components of the on-site controller 144. In thepresent embodiment, a drilling model class is defined to capture anddefine the drilling state throughout the drilling process. The class mayinclude real time information. This class may be based on the followingcomponents and sub-models: a drill bit model, a borehole model, a rigsurface gear model, a mud pump model, a WOB/differential pressure model,a positional/rotary model, an MSE model, an active well plan, andcontrol limits. The class may produce a control output solution and maybe executed via a main processing loop that rotates through the variousmodules of the GCL 914.

The drill bit model may represent the current position and state of thedrill bit. This model includes a three dimensional position, a drill bittrajectory, BHA information, bit speed, and toolface (e.g., orientationinformation). The three dimensional position may be specified innorth-south (NS), east-west (EW), and true vertical depth (TVD). Thedrill bit trajectory may be specified as an inclination and an azimuthangle. The BHA information may be a set of dimensions defining theactive BHA. The borehole model may represent the current path and sizeof the active borehole. This model includes hole depth information, anarray of survey points collected along the borehole path, a gamma log,and borehole diameters. The hole depth information is for the currentdrilling job. The borehole diameters represent the diameters of theborehole as drilled over the current drill job.

The rig surface gear model may represent pipe length, block height, andother models, such as the mud pump model, WOB/differential pressuremodel, positional/rotary model, and MSE model. The mud pump modelrepresents mud pump equipment and includes flow rate, standpipepressure, and differential pressure. The WOB/differential pressure modelrepresents drawworks or other WOB/differential pressure controls andparameters, including WOB. The positional/rotary model represents topdrive or other positional/rotary controls and parameters includingrotary RPM and spindle position. The active well plan represents thetarget borehole path and may include an external well plan and amodified well plan. The control limits represent defined parameters thatmay be set as maximums and/or minimums. For example, control limits maybe set for the rotary RPM in the top drive model to limit the maximumRPMs to the defined level. The control output solution represents thecontrol parameters for the drilling rig 110.

The main processing loop can be handled in many different ways. Forexample, the main processing loop can run as a single thread in a fixedtime loop to handle rig sensor event changes and time propagation. If norig sensor updates occur between fixed time intervals, a time onlypropagation may occur. In other embodiments, the main processing loopmay be multi-threaded.

Each functional module of the GCL 914 may have its behavior encapsulatedwithin its own respective class definition. During its processingwindow, the individual units may have an exclusive portion in time toexecute and update the drilling model. For purposes of example, theprocessing order for the modules may be in the sequence of geo modifiedwell planner 1104, build rate predictor 1102, slide estimator 1108,borehole estimator 1106, error vector calculator 1110, slide planner1114, convergence planner 1116, geological drift estimator 1112, andtactical solution planner 1118. It is understood that other sequencesmay be used.

In the present embodiment, the GCL 914 may rely on a programmable timermodule that provides a timing mechanism to provide timer event signalsto drive the main processing loop. While the on-site controller 144 mayrely purely on timer and date calls driven by the programmingenvironment (e.g., java), this would limit timing to be exclusivelydriven by system time. In situations where it may be advantageous tomanipulate the clock (e.g., for evaluation and/or testing), theprogrammable timer module may be used to alter the time. For example,the programmable timer module may enable a default time set to thesystem time and a time scale of 1.0, may enable the system time of theon-site controller 144 to be manually set, may enable the time scalerelative to the system time to be modified, and/or may enable periodicevent time requests scaled to the time scale to be requested.

Referring to FIG. 12, one embodiment of the ACL 916 provides differentfunctions to the on-site controller 144. The ACL 916 may be considered asecond feedback control loop that operates in conjunction with a firstfeedback control loop provided by the GCL 914. The ACL 916 may alsoprovide actual instructions to the drilling rig 110, either directly tothe drilling equipment 216 or via the control systems 208, 210, and 212.The ACL 916 may include a positional/rotary control logic block 1202,WOB/differential pressure control logic block 1204, fluid circulationcontrol logic block 1206, and a pattern recognition/error detectionblock 1208.

One function of the ACL 916 is to establish and maintain a targetparameter (e.g., an ROP of a defined value of ft/hr) based on input fromthe GCL 914. This may be accomplished via control loops using thepositional/rotary control logic block 1202, WOB/differential pressurecontrol logic block 1204, and fluid circulation control logic block1206. The positional/rotary control logic block 1202 may receive sensorfeedback information from the input driver 902 and set point informationfrom the GCL 914 (e.g., from the tactical solution planner 1118). Thedifferential pressure control logic block 1204 may receive sensorfeedback information from the input driver 902 and set point informationfrom the GCL 914 (e.g., from the tactical solution planner 1118). Thefluid circulation control logic block 1206 may receive sensor feedbackinformation from the input driver 902 and set point information from theGCL 914 (e.g., from the tactical solution planner 1118).

The ACL 916 may use the sensor feedback information and the set pointsfrom the GCL 914 to attempt to maintain the established targetparameter. More specifically, the ACL 916 may have control over variousparameters via the positional/rotary control logic block 1202,WOB/differential pressure control logic block 1204, and fluidcirculation control logic block 1206, and may modulate the variousparameters to achieve the target parameter. The ACL 916 may alsomodulate the parameters in light of cost-driven and reliability-drivendrilling goals, which may include parameters such as a trajectory goal,a cost goal, and/or a performance goal. It is understood that theparameters may be limited (e.g., by control limits set by the drillingengineer 306) and the ACL 916 may vary the parameters to achieve thetarget parameter without exceeding the defined limits. If this is notpossible, the ACL 916 may notify the on-site controller 144 or otherwiseindicate that the target parameter is currently unachievable.

In some embodiments, the ACL 916 may continue to modify the parametersto identify an optimal set of parameters with which to achieve thetarget parameter for the particular combination of drilling equipmentand formation characteristics. In such embodiments, the on-sitecontroller 144 may export the optimal set of parameters to the database128 for use in formulating drilling plans for other drilling projects.

Another function of the ACL 916 is error detection. Error detection isdirected to identifying problems in the current drilling process and maymonitor for sudden failures and gradual failures. In this capacity, thepattern recognition/error detection block 1208 receives input from theinput driver 902. The input may include the sensor feedback received bythe positional/rotary control logic block 1202, WOB/differentialpressure control logic block 1204, and fluid circulation control logicblock 1206. The pattern recognition/error detection block 1208 monitorsthe input information for indications that a failure has occurred or forsudden changes that are illogical.

For example, a failure may be indicated by an ROP shift, a radicalchange in build rate, or any other significant changes. As anillustration, assume the drilling is occurring with an expected ROP of100 ft/hr. If the ROP suddenly drops to 50 ft/hr with no change inparameters and remains there for some defined amount of time, anequipment failure, formation shift, or another event has occurred.Another error may be indicated when MWD sensor feedback has beensteadily indicating that drilling has been heading north for hours andthe sensor feedback suddenly indicates that drilling has reversed in afew feet and is heading south. This change clearly indicates that afailure has occurred. The changes may be defined and/or the patternrecognition/error detection block 1208 may be configured to watch fordeviations of a certain magnitude. The pattern recognition/errordetection block 1208 may also be configured to detect deviations thatoccur over a period of time in order to catch more gradual failures orsafety concerns.

When an error is identified based on a significant shift in inputvalues, the on-site controller 201 may send an alert. This enables anindividual to review the error and determine whether action needs to betaken. For example, if an error indicates that there is a significantloss of ROP and an intermittent change/rise in pressure, the individualmay determine that mud motor chunking has likely occurred with rubbertearing off and plugging the bit. In this case, the BHA may be trippedand the damage repaired before more serious damage is done. Accordingly,the error detection may be used to identify potential issues that areoccurring before they become more serious and more costly to repair.

Another function of the ACL 916 is pattern recognition. Patternrecognition is directed to identifying safety concerns for rig workersand to provide warnings (e.g., if a large increase in pressure isidentified, personnel safety may be compromised) and also to identifyingproblems that are not necessarily related to the current drillingprocess, but may impact the drilling process if ignored. In thiscapacity, the pattern recognition/error detection block 1208 receivesinput from the input driver 902. The input may include the sensorfeedback received by the positional/rotary control logic block 1202,WOB/differential pressure control logic block 1204, and fluidcirculation control logic block 1206. The pattern recognition/errordetection block 1208 monitors the input information for specific definedconditions. A condition may be relatively common (e.g., may occurmultiple times in a single borehole) or may be relatively rare (e.g.,may occur once every two years). Differential pressure, standpipepressure, and any other desired conditions may be monitored. If acondition indicates a particular recognized pattern, the ACL 916 maydetermine how the condition is to be addressed. For example, if apressure spike is detected, the ACL 916 may determine that the drillingneeds to be stopped in a specific manner to enable a safe exit.Accordingly, while error detection may simply indicate that a problemhas occurred, pattern recognition is directed to identifying futureproblems and attempting to provide a solution to the problem before theproblem occurs or becomes more serious.

Referring to FIG. 13, one embodiment of a computer system 1300 isillustrated. The computer system 1300 is one possible example of asystem component or device such as the on-site controller 144 of FIG.1A. In scenarios where the computer system 1300 is on-site, such as atthe location of the drilling rig 110 of FIG. 1A, the computer system maybe contained in a relatively rugged, shock-resistant case that ishardened for industrial applications and harsh environments.

The computer system 1300 may include a central processing unit (“CPU”)1302, a memory unit 1304, an input/output (“I/O”) device 1306, and anetwork interface 1308. The components 1302, 1304, 1306, and 1308 areinterconnected by a transport system (e.g., a bus) 1310. A power supply(PS) 1312 may provide power to components of the computer system 1300,such as the CPU 1302 and memory unit 1304. It is understood that thecomputer system 1300 may be differently configured and that each of thelisted components may actually represent several different components.For example, the CPU 1302 may actually represent a multi-processor or adistributed processing system; the memory unit 1304 may includedifferent levels of cache memory, main memory, hard disks, and remotestorage locations; the I/O device 1306 may include monitors, keyboards,and the like; and the network interface 1308 may include one or morenetwork cards providing one or more wired and/or wireless connections toa network 1314. Therefore, a wide range of flexibility is anticipated inthe configuration of the computer system 1300.

The computer system 1300 may use any operating system (or multipleoperating systems), including various versions of operating systemsprovided by Microsoft (such as WINDOWS), Apple (such as Mac OS X), UNIX,and LINUX, and may include operating systems specifically developed forhandheld devices, personal computers, and servers depending on the useof the computer system 1300. The operating system, as well as otherinstructions (e.g., software instructions for performing thefunctionality described in previous embodiments) may be stored in thememory unit 1304 and executed by the processor 1302. For example, if thecomputer system 1300 is the on-site controller 144, the memory unit 1304may include instructions for performing methods such as the methods 600of FIG. 6, 700 of FIG. 7A, 720 of FIG. 7B, 800 of FIG. 8A, 820 of FIG.8B, 830 of FIG. 8C, and 840 of FIG. 8D.

Referring to FIGS. 14A-14D, embodiments of sections of the borehole 164of FIG. 1B are illustrated. FIG. 14A illustrates an embodiment of theborehole 164 where the slide occurs in the middle of the section. Theslide is planned to begin at a point marked by line 1402 and end at apoint marked by line 1404. Sequential survey points 1406 and 1408 marklocations where measured surveys occur. Being sequential, there is nosurvey point between the two survey points 1406 and 1408. FIG. 14Billustrates an embodiment of the borehole 164 a where the slide occursat the beginning of the section (e.g., right after the survey point1406). FIG. 14C illustrates an embodiment of the borehole 164 b wherethe slide occurs at the end of the section (e.g., leading up to thesurvey point 1408). FIG. 14D illustrates an embodiment of the borehole164 c where the slide occurs for the entire distance between the surveypoints 1406 and 1408. FIG. 14E illustrates the boreholes 164 a-164 c(not to scale) overlaid on one another.

Referring specifically to FIG. 14A, in the present example, two possiblepaths 1410 and 1412 are illustrated between the survey points 1406 and1408. The two paths 1410 and 1412 are used herein to illustrate what mayhappen in the borehole 164 between the two survey points 1406 and 1408.As described previously, surveys may occur at defined intervals, such asevery thirty, forty-five, or ninety feet. For example, a survey mayoccur each time a new section of pipe (e.g., a joint) is added to thedrill string. If the sections are approximately thirty feet long and asurvey is taken every three sections (e.g., a stand), the surveys mayoccur approximately every ninety feet. Constant surveying is generallynot practical as performing a survey may take a relatively substantialamount of time (e.g., from five to twenty minutes) and, in addition,control of the reactional torque neutral point may be lost. Betweensurveys, the state of the drilling (e.g., orientation of the bit anddistance drilled) is not generally known. Accordingly, the path betweenthe survey points 1406 and 1408 is unknown. This lack of knowledge mayaffect various aspects of drilling the borehole 164, as well as thefinal efficiency of the well.

For example, assume that the planned borehole 164 includes a fifty footslide (from point 1402 to point 1404) and the slide occurs between thesurvey points 1406 and 1408. One possible path 1410 for the slide occurswhen the drilling is held almost perfectly on course, which would resultin a slide of approximately fifty feet (assuming other factors areideal). However, another possible path 1412 occurs when the drillingdoes not stay on course. In the present example, the path 1412 is noteven on course prior to the line 1402 that represents the beginning ofthe slide. As the shortest distance between the points 1406 and 1408 isa straight line (or an arc at the maximum build rate), the path 1410 ismore efficient than the path 1412 in making progress toward the target.Furthermore, not only is the path 1412 less efficient in reaching thetarget, it also forms a less ideal borehole in terms of tortuosity asdescribed in greater detail below.

It is understood, as described previously, that there may be a surveypoint offset where the survey point is actually located some distancebehind the bit and so the survey location may not represent the actualbit location. Because of this offset distance, a survey is accurate onlyto a certain distance (e.g., fifty feet behind the bit) and there isusually some uncertainty in the path ahead of the survey point to wherethe bit is actually located. Accordingly, knowing the actual path past asurvey point may also be beneficial as illustrated by path segment 1413extending from survey point 1408.

In addition to providing information about drilling efficiency, knowingwhat occurs between the survey points 1406 and 1408 may enable theeffective build rate of the BHA to be assessed more objectively becausethe build rate orientation stability can be taken into account. If thebuild rate orientation stability is not taken into account, the secondpath 1412 that lacks orientation stability may be included in theassessment, which would make the BHA seem less efficient than itactually was. In turn, the more accurate assessment of the actual pathof the BHA aids in the accuracy of later drilling predictions (e.g.,build rate predictions).

Knowledge of what occurs between survey points may also aid inaddressing drilling problems such as tortuosity in the borehole that mayimpact whether casing can be run, increase friction in the drill string,affect lubrication planning for slides, and other issues. For example,dogleg severity is often viewed as the change of angle between twosequential survey points. However, this view provides no information asto whether a dogleg exists between the survey points and, if one doesexist, how severe it is. Furthermore, the orientation of the doglegs maycreate even more severe problems. For example, a dogleg created by aleft arc that is immediately followed by a dogleg created by a right arcmay be more problematic than if the following dogleg is also a left arc.In other words, sequential doglegs that arc in generally the samedirection may be preferable to sequential doglegs that arc in oppositedirections. Accordingly, the survey points may show a doglegcharacterized by a five degree per hundred foot severity (5°/100′),while the actual path may include a dogleg of 10°/100′ at one point,5°/100′ at another point, et cetera, between the survey points, andthese doglegs may have different orientations.

Knowing what is happening between the survey points and accumulatingsuch information over the course of the well enables problems to beaddressed by implementing one or more solutions before drillingcontinues, during later drilling, and even after drilling. For example,the ability to measure tortuosity in real time or near real time mayenable determinations to be made during drilling such as whetherlubrication is needed, how and when to apply the lubrication, andwhether back reaming a particular section of the borehole is needed.Such information may also be used to determine whether a planned wellshould be stopped early. After the well is completed, the use of pathinformation that is higher resolution than the information provided bythe survey points may be used to improve the well, such as in adetermination on where to focus reaming activity (e.g., at a problemarea at ten thousand feet).

It is understood that information about what is occurring between surveypoints may also be useful even when not sliding. For example, driftcaused by formation characteristics may affect the path even whendrilling straight ahead. Accordingly, current location estimates may beuseful regardless of the type of drilling (e.g., rotating or sliding).

Referring to FIG. 15, one embodiment of a three-dimensional boreholespace 1500 is illustrated with two measured survey points 1502 (alsolabeled as “A”) and 1504 (also labeled as “C”). A borehole path (notshown) extends between the two survey points 1502 and 1504, but theactual path is unknown. Current borehole projection methods frequentlyuse a minimum curvature technique for estimating the borehole projectionbetween the two survey points 1502 and 1504. Assuming the initialborehole position is known as well as its initial survey trajectory,there may be only a subsequent measure of additional borehole length anda new survey trajectory that can be measured from surface and downholeinstruments that are available.

In FIG. 15, the borehole space is presented in Cartesian space with aNorth-South (N) axis 1508, an East-West (E) axis 1510, an Up-DownVertical (V) axis 1512, and a borehole trajectory where an inclinationangle represents the vertical component and a compass style azimuthangle represents the horizontal component. The initial survey point 1502has an inclination and azimuth trajectory of α1 and ε1, respectively,and the second survey point 1504 has an inclination and azimuthtrajectory of α2 and ε2, respectively.

With only new survey trajectory and path length information available,an assumption must be made about the shape of the borehole between thesurvey points 1502 and 1504. The minimum curvature method works off theassumption that the borehole moves along the smoothest possible arcbetween two survey points. This arc is represented by arc 1514. Thechange in trajectory angle from survey point 1502 to survey point 1504(β) is often referred to as a dogleg in the context of surveying. Thepath ABC (where B is also labeled as point 1506) represents the balancedtangential method path, whereby a borehole projection is estimated bytwo line segments which intersect at the point where the curvatureangle, β, is evenly bisected. This bisection point is point 1506 in thepresent example. This is a useful case, as the minimum curvature methodrepresents a special case of the balanced tangential method where thetwo line segments are substituted with a circular arc curve (e.g., thearc 1514) that also passes through points 1502 and 1504 with tangents atthose points aligned with their respective trajectories. The equationsfor the curve AB are the same as the balanced tangential method forcalculating path ABC except for the application of the ratio factor(RF):

$\begin{matrix}{\mspace{79mu}{{\Delta\; V} = {{\frac{\Delta MD}{2}\left\lbrack {{\cos\mspace{14mu}{\alpha 1}} + {\cos\mspace{14mu}{\alpha 2}}} \right\rbrack} \times R\; F}}} & \left( {{Equation}\mspace{14mu} 1} \right) \\{{\Delta\; N} = {{\frac{\Delta MD}{2}\left\lbrack {{\sin\mspace{14mu}{\alpha 1} \times \cos\mspace{14mu}{ɛ1}} + {\sin\mspace{14mu}{\alpha 2} \times \cos\mspace{14mu}{ɛ2}}} \right\rbrack} \times R\; F}} & \left( {{Equation}\mspace{14mu} 2} \right) \\{\mspace{79mu}{\Delta\; E{\frac{\Delta\; M\; D}{2}\left\lbrack {{\sin\mspace{14mu}{\alpha 1} \times \sin\mspace{14mu}{ɛ1}} + {\sin\mspace{14mu}{\alpha 2} \times \sin\mspace{14mu}{ɛ2}}} \right\rbrack} \times R\; F}} & \left( {{Equation}\mspace{14mu} 3} \right)\end{matrix}$

When using Equations 1-3 for estimating borehole positions betweenmeasured survey points, ΔMD represents an increase in measured depthprogress between two survey trajectory measurements.

The ratio factor (RF) is used to account for the path length differencebetween the length of ABC and the length of the minimum curvature arcwhich crosses through AC. RF is given by the equation:

$\begin{matrix}{{RF} = {\frac{2}{\beta}\tan\frac{\beta}{2}}} & \left( {{Equation}\mspace{14mu} 4} \right)\end{matrix}$

The minimum curvature method may result in significant inaccuracy asshown in the following examples. There are two basic assumptions inthese examples. The first is that the example starts from a ninetydegree inclination. The second is that all sliding is two-dimensional inthe vertical plane.

Table 1, shown below, illustrates a scenario where a slide has occurred.

TABLE 1 Description Value Units Total MD Increment Between Surveys 100ft Slide/Build Duration 15 ft Instantaneous Build Rate 12 Degrees/100 ftInclination Change 1.8 Degrees

For purposes of illustration, the distance between surveys is equal toone hundred feet and is used as a surface measurement of the totalmeasured depth increment. Accordingly, the total measured depthincrement between surveys in Table 1 is one hundred feet. The slidelasted for fifteen feet and had an instantaneous build rate of twelvedegrees per one hundred feet, so the inclination change over the twelvefoot slide was 1.8 degrees.

Table 2, shown below, illustrates two scenarios where a slide hasoccurred. The first column contains two rows, with each row indicatingwhether the slide occurred at the beginning of the one hundred footdistance (one embodiment of which is illustrated in FIG. 14B) or at theend (one embodiment of which is illustrated in FIG. 14C).

TABLE 2 Interpreted Traditional Formation Dip Curve Fit Error Over MDTVD TVD Interpreted Survey Period change change change TVD error Due toTVD (ft) (ft) (ft) (ft) Error (degrees) Slide 100 2.906 1.571 1.3350.765 before Rotate Rotate 100 0.236 1.571 −1.335 −0.765 before Slide

In the first row where sliding occurred before rotation, the TVD changeis 2.906 feet. Using the previously presented equations for curvefitting, the curve fit TVD change is 1.571 feet. This results in aninterpreted TVD error of 1.335 feet and an interpreted formation diperror of 0.765 degrees. In the second row where sliding occurred afterrotation, the TVD change is 0.236 feet. Using the previously presentedequations for curve fitting, the curve fit TVD change is 1.571 feet. Inother words, the curve fit TVD change is the same as in row one. Thecurve fit TVD change of 1.571 results in an interpreted TVD error of−1.335 feet and an interpreted formation dip error of −0.765 degrees.

Although the errors may cancel each other out relative to the entirewell (e.g., an error in one direction may be canceled by an equal errorin the opposite direction), the errors in a given direction accumulateand there is more accumulation the longer that a slide occurs in aparticular direction.

As illustrated in Table 2, the curve fit TVD change for a particular setof slide/build duration and instantaneous build rate values remainsconstant regardless of whether sliding occurs before or after rotationeven though the TVD change is different based on whether sliding occursbefore or after rotation. This difference between the curve fit TVDchange and the total TVD change occurs for different values ofslide/build duration and instantaneous build rate in Table 1. The curvefit TVD change and the total TVD change may only match in two scenarios.The first is when the slide occurs for the full one hundred feet (e.g.,slide/build duration is set to 100 in Table 1), as the borehole shapemay be estimated as an arc between the two survey points (one embodimentof which is illustrated in FIG. 14D). The second is when the slide issymmetrically centered on the midpoint between survey points. Asillustrated in FIG. 14E, the boreholes 164 a-164 c of FIGS. 14B-14D mayvary significantly for the same curve fit TVD change.

Accordingly, using only information from two measured survey points toestimate the state of the drilling (e.g., orientation of the bit anddistance drilled) between the two survey points may result insignificant inaccuracies. These inaccuracies may negatively impactdrilling efficiency, the ability to objectively identify well plancorrections, the ability to characterize formation position and dipangles, and/or similar issues. Furthermore, problems such as tortuositymay be more difficult to identify and address. Inaccurate TVDinformation may result in difficulties in following the target layer(e.g., the layer 172A of FIG. 1B), as even seemingly minor variations ininclination (e.g., one half of one degree) may cause the drill bit toexit the target layer.

Referring to FIG. 16, a method 1600 illustrates one embodiment of aprocess that may be executed by the on-site controller 144 of FIG. 2Aand/or another part of the surface steerable system 201. For example,software instructions needed to execute the method 1600 may be stored ona computer readable storage medium of the on-site controller 144 andthen executed by the processor 412 that is coupled to the storage mediumand is also part of the on-site controller 144.

In the present example, the method 1600 may be used to estimate theposition of the drill bit between survey points during straight drillingand/or during a sliding operation. The method 1600 may provide moreaccurate information on the state of the drilling (e.g., orientation ofthe bit and distance drilled) than that provided by the minimumcurvature method described above.

In step 1602, toolface and other non-survey sensor information isreceived. The toolface information may be relayed from the toolfaceperiodically, such as at set intervals of between ten and thirtyseconds. The non-survey sensor information may include any type of data,such as differential pressure and may be continuous or non-continuous.As the toolface information may be obtained at set intervals and theother non-survey sensor information may be continuous, non-survey sensorinformation may be obtained between orientation updates. The non-surveysensor information may be averaged (symmetrically or otherwise) torelate the sensor information to the toolface information.

In step 1604, calculations are performed on the non-survey sensorinformation to estimate the amount of progress made by the drill bitsince the last estimate. For example, the differential pressure may beused to estimate the force on the bit, which may be used with formationinformation to determine the distance that the bit should have drilledin the current formation layer.

One difficulty in measuring drilling information between survey pointsis that measurements made at the top of the drill string may notaccurately reflect events at the BHA. For example, a ten thousand footdrill string may be viewed as a big spring, and when motion is stoppedat the surface, the spring force may continue to increase the length ofthe drill string and the BHA may make progress in a certain direction.In another example, if a foot of pipe is moved into the hole, the drillstring may compress and/or buckle and the bit may move little, if atall.

Accordingly, predictions about the current orientation and progress ofthe drill bit may vary in accuracy depending on the information on whichthe predictions are based. For example, rather than exclusively usingsurface deviation, energy produced by the bit and a combination ofdifferential pressure, MSE, and/or other measurements may be used. Insome embodiments, more sensors may be placed downhole to provide moreaccurate information. Depending on the particular embodiment,calculations may be performed based on sensors at various levels of thedrillstring to predict actual progress between surveys. For example,calculations may be used to approximate the fluid pressure to how muchforce is on the bit. Other calculations may be made to account for drillstring compression, tension, and/or buckling.

It is understood that the calculations may differ based on theconfiguration of the drilling equipment and/or the BHA. For example, ifan autodrilling system is used, the drilling rig may have a fixed valuefor ROP, WOB, DP, and/or other characteristics. Such fixed values mayaffect the particular calculations used. For example, if DP is fixed,the calculations may not rely on changes in DP as the autodrillingsystem may attempt to maintain the fixed DP value. In another example,if ROP is fixed, measurements of DP may have a wide range due to theattempt to maintain the fixed ROP value. If an autodrilling system isnot used to control drilling functions, more flexibility may beavailable in the calculations that are used.

In step 1606, calculations may be performed to obtain an estimate of theBHA's location using the toolface information and the calculated amountof progress. This calculation may be performed in a variety of ways,including the calculation of a vector as a three-dimensional estimate ofthe drill bit's current location and orientation. The vector progress(e.g., degrees/100 feet) may come from the build rate predictor 1102 ofFIG. 11, and may also include the use of formation information.

In step 1608, a determination may be made as to whether survey data hasbeen received. If not, the method 1600 may return to step 1602 andcalculate another location estimate (e.g., another vector) of the BHA'sincremental progression. As these estimates are calculated, an estimatedpath of the BHA between the two survey points is developed. If surveydata has been received, the method 1600 moves to step 1610, where thesurvey data is used to update the estimated location. The method 1600may then return to step 1602 and calculate another location estimateusing the new survey data as the baseline for the current estimate.

Accordingly, the survey data may serve as truth data against which theestimates can be measured. This enables the calculations used for theestimates to be refined in conjunction with formation information asmore survey point data is received. For example, if the estimates use aparticular drilling speed through the current formation layer and thesurvey data indicates that the drilling speed is incorrect, futureestimates may be calculated based on the revised drilling speed toprovide a higher level of accuracy. Furthermore, although not shown inFIG. 16, it is understood that the survey data may also be used to checkthe estimated build rate and, if needed, recalibrate the build rate(e.g., the build rate predictor 1102 of FIG. 11) to correspond to thesurvey data.

Referring to FIG. 17, a method 1700 illustrates one embodiment of aprocess that may be executed by the on-site controller 144 of FIG. 2Aand/or another part of the surface steerable system 201. For example,software instructions needed to execute the method 1700 may be stored ona computer readable storage medium of the on-site controller 144 andthen executed by the processor 412 that is coupled to the storage mediumand is also part of the on-site controller 144. In the present example,the method 1700 illustrates a more detailed example of steps 1602-1606of FIG. 16.

In step 1702, the average differential pressure is determined for atoolface update period (e.g., the length of time between toolfaceupdates). The differential pressure may be acquired or calculated. Thetoolface update period may vary based on factors such as the speed atwhich the MWD component is set to run, the priority given to thetoolface information in the MWD component, the overall bandwidthavailable to the MWD component, and/or other factors.

In step 1704, the average ROP is determined. For example, thedifferential pressure determined in step 1702 may be used to assist in adatabase lookup. More specifically, the average ROP for the currentformation using the current BHA at the average differential pressure maybe acquired from the database.

In step 1706, the average ROP is applied over the toolface update periodto determine the borehole distance increase since the last iteration.For example, if the ROP retrieved from the database indicates that theROP is fifty feet per hour and the toolface update period is thirtyseconds, then the distance increase should be approximately five inches.

In steps 1708 and 1710, the new toolface sample is used to derive aplane of arc to use in a curvature projection. In the current example,applying observations from the previously described minimum curvaturemethod may be useful when developing a method for estimating boreholeposition and trajectory from toolface measurements between surveymeasurements. Certain parameters used in the minimum curvature methodmay be estimated instead of directly measured.

With additional reference to FIG. 18, one embodiment of atwo-dimensional borehole space 1800 illustrates the minimum curvaturepath 1801 in the plane of the curvature arc. The space 1800 isillustrated with two measured survey points 1802 (also labeled as “A”)and 1804 (also labeled as “C”).

As illustrated in FIG. 18, the angle β can be seen intuitively as thearc angle along which the minimum curvature path is made and the changein trajectory between the two path points. Angle β would normally becalculated from survey trajectory angles using an additional formula. Inthe context of directional well steering where the angle β isdeliberately controlled, it can also be considered an angle of desiredor target build. In the case of projecting build in real time, aninstantaneous β estimate may be needed. The complexity of such anestimate may vary. For example, a relatively simple approach may use ageometric formula of BHA dimensions. In other examples, more detailedapproaches may account for factors from previous and instantaneous rigsensor data, formation data, etc., in order to provide an improvedprediction of an instantaneous build rate while drilling. The build ratepredictor 1102 of FIG. 11 may provide a functional component used toperform this task within the surface steerable system 201.

In the minimum curvature method, AMD may be directly obtained from thesurface measurement of the difference in drill string lengths betweensurveys. When accounting for the position of the bit, this method ofusing surface changes in drill string lengths may be used in arelatively simple approach for an estimate. However, accounting fordrill string tension, compression, buckling, and other factors thatimpact drill string length may provide a better estimate of the currentdrill bit position as it is drilling new borehole.

In the case of updating borehole trajectory over a given change inborehole depth, survey measurements may be used when available. In suchcases, one goal of slide estimation may be to estimate trajectory alongthe bit path by using toolface history along the intervals ahead ofwhere survey data is available to allow a real time or near real timeestimate of bit location.

With additional reference to FIG. 19, one embodiment of atwo-dimensional borehole space 1900 illustrates slide estimation byintegration of a single toolface measurement using the minimum curvaturepath 1801 of FIG. 18. More specifically, the present example addressesthe application of a toolface vector 1902 that is a direct linearprojection of an individual toolface. This projection is overlaidagainst the minimum curvature path 1801 for purposes of illustration. Itis understood that while the present example uses a gravity toolfaceframe of reference, magnetic references can also be used with variationsin some formulas described below to account for the use of magneticreferences.

In this case, the borehole is assumed to be moving in a straight pathalong the trajectory AB until encountering a measured toolface. Uponencountering the toolface at point 1806 (B), the toolface is applieddirectly to the trajectory BC as follows:

α2=α1+cos TF×β  (Equation 5)

ε2=ε1+sin TF×β  (Equation 6)

where TF is the toolface vector angle presented relative to the gravity“up” vector. The position estimates for the path between AC may be givenby:

ΔV=ΔBD×cos α1  (Equation 7)

ΔN=ΔBD×[sin α1×cos ε1]  (Equation 8)

ΔE=ΔBD×[sin α1×sin ε1]  (Equation 9)

The equations 7-9 represent the simple projection of the straight lineAB in Cartesian space since the toolface would not be applied untilpoint B. When overlaid on the curvature model, it is evident that thisestimate is analogous to the balanced tangential method where thestarting and finishing points A and C and the path ABC lie apart fromthe overlying smooth circular arc.

With additional reference to FIG. 20, one embodiment of thetwo-dimensional borehole space 1900 of FIG. 19 is illustrated using theminimum curvature concept to yield a better estimate of actual boreholedisplacement by modeling the borehole as an arc rather than bending linesegments. When framed as a single arc curve displacement 2002, theprojection of the single toolface may appear as illustrated in FIG. 20.

In this case, the toolface influence on trajectory may be modeled toyield the same tangent trajectory from the toolface build vector 1902 asfollows:

α2=α1+cos TF×β  (Equation 10)

ε2=ε1+sin TF×β  (Equation 11)

After deriving trajectory changes, the minimum curvature methodequations are again applicable for determining the positionaldisplacements over the interval as follows:

$\begin{matrix}{\mspace{79mu}{{\Delta\; V} = {{\frac{\Delta BD}{2}\left\lbrack {{\cos\mspace{14mu}{\alpha 1}} + {\cos\mspace{14mu}{\alpha 2}}} \right\rbrack} \times R\; F}}} & \left( {{Equation}\mspace{14mu} 12} \right) \\{{\Delta\; N} = {{\frac{\Delta BD}{2}\left\lbrack {{\sin\mspace{14mu}{\alpha 1} \times \cos\mspace{14mu}{ɛ1}} + {\sin\mspace{14mu}{\alpha 2} \times \cos\mspace{14mu}{ɛ2}}} \right\rbrack} \times R\; F}} & \left( {{Equation}\mspace{14mu} 13} \right) \\{\mspace{79mu}{{\Delta\; E} = {{\frac{\Delta BD}{2}\left\lbrack {{\sin\mspace{14mu}{\alpha 1} \times \sin\mspace{14mu}{ɛ1}} + {\sin\mspace{14mu}{a2} \times \sin\mspace{14mu}{ɛ2}}} \right\rbrack} \times R\; F}}} & \left( {{Equation}\mspace{14mu} 14} \right)\end{matrix}$

In this case, the line path to arc relationship works out to be the sameas the minimum curvature RF:

$\begin{matrix}{{RF} = {\frac{2}{\beta}\tan\frac{\beta}{2}}} & \left( {{Equation}\mspace{14mu} 15} \right)\end{matrix}$

While the preceding example illustrates slide estimation by integrationof a single toolface measurement, it is understood that a range oftoolface measurements may be used. As described above, the integrationof individual toolface projections may provide a useful method of slideand borehole estimation on a near real time basis. However, like the useof minimum curvature on a smaller scale, this process may be subject tocumulative errors over longer intervals. Accordingly, a range oftoolfaces may be used over an interval to address this issue. Forexample, the range of toolfaces may be used to provide a net effectivetoolface direction and a net effective build rate angle may also beestimated. In both cases, the benefit of larger data sets (e.g.,toolface histories) may enable the application of more sophisticatedstatistical methods and filtering techniques. For example, over a pathinterval, a target toolface may be desired and attempted to bemaintained. In practice, the ability to control the toolface over theseintervals can be evaluated in statistical metrics, like a circulardistribution. These metrics can then be used to refine the effectivebuild rate and toolface direction over the evaluation interval.

Referring again specifically to FIG. 17, in step 1712, an updatedspatial estimate of the borehole position may be estimated based on thepreceding steps. The estimated spatial estimate may be provided to thedisplay 250 of FIG. 2B (e.g., for display to the driller 310 of FIG. 3),provided as feedback to the convergence planner 1116 of FIG. 11, and/orotherwise used.

Referring to FIG. 21, a method 2100 illustrates one embodiment of aprocess that may be executed by the on-site controller 144 of FIG. 2Aand/or another part of the surface steerable system 201. For example,software instructions needed to execute the method 2100 may be stored ona computer readable storage medium of the on-site controller 144 andthen executed by the processor 412 that is coupled to the storage mediumand is also part of the on-site controller 144. In the present example,the method 2100 may provide a more detailed example of steps 1602-1606of FIG. 16.

In step 2102, the increase in measured depth is determined for thetoolface update period. The increase may be acquired or calculated. Forexample, the measured depth may be acquired based on a surfacemeasurement of the length of pipe inserted into the borehole between thelast toolface update period and the current toolface update period. Inother examples, the measured depth may be calculated based onmeasurements received from downhole sensors.

In step 2104, the method 2100 may account for deviations in the overalldrillstring length due to issues such as compression, tension, and/orbuckling. In some embodiments, step 2104 may be omitted and the measureddepth determined in step 2102 may be used with accounting for suchdeviations. Steps 2106, 2108, and 2110 may similar or identical to steps1708, 1710, and 1712, respectively, with the estimate using theinformation from steps 2102 and 2104.

Referring to FIG. 22, a method 2200 illustrates one embodiment of aprocess that may be executed by the on-site controller 144 of FIG. 2Aand/or another part of the surface steerable system 201. For example,software instructions needed to execute the method 2200 may be stored ona computer readable storage medium of the on-site controller 144 andthen executed by the processor 412 that is coupled to the storage mediumand is also part of the on-site controller 144. In the present example,the method 2200 may provide a more detailed example of step 2104 of FIG.21, although it is understood that the method 2200 may be used with theother methods described herein.

In step 2202, a hookload measurement is acquired and compared to thestatic weight of the drill string vertical section excluding the mass ofthe surface equipment. The static weight of the drill string verticalsection excluding the mass of the surface equipment may be determined,for example, from information available from the local database 912 ofFIG. 9 and/or regional database 128 of FIG. 1A.

In step 2204, the tensile elastic deformation of the drill stringcomponents in the vertical section is determined. This determination mayuse, for example, average cross-section and mechanical properties of thedrill string components in the vertical section. The averagecross-section and mechanical properties may be determined, for example,from information available from the local database 912 of FIG. 9 and/orregional database 128 of FIG. 1A.

In step 2206, a real time or near real time WOB value is determined. Forexample, the WOB value may be obtained using a downhole sensor. Inanother example, the WOB value may be approximated using differentialpressure and mud motor properties.

In step 2208, the compressive elastic deformation of the drill stringcomponents in the horizontal section of the borehole (if any) isdetermined. This determination may use, for example, averagecross-section and mechanical properties of the drill string componentsin the vertical section. The average cross-section and mechanicalproperties may be determined, for example, from information availablefrom the local database 912 of FIG. 9 and/or regional database 128 ofFIG. 1A.

In step 2210, the total drill string length dynamic offset from themeasured depth is determined. This total length dynamic offset accountsfor variations between the measured depth and the actual drillstringlength due to issues such as compression, tension, and/or buckling inthe drillstring.

Referring to FIG. 23 and with additional reference to FIGS. 24 and 25, amethod 2300 illustrates one embodiment of a process that may be executedby the on-site controller 144 of FIG. 2A and/or another part of thesurface steerable system 201. For example, software instructions neededto execute the method 2300 may be stored on a computer readable storagemedium of the on-site controller 144 and then executed by the processor412 that is coupled to the storage medium and is also part of theon-site controller 144.

In step 2302, information is received by the surface steerable system201. The information may be any type of information displayed by thedisplay 250. For purposes of example, the information may include theorientation and progress estimate from FIG. 16.

In step 2304, the GUI (e.g., the circular chart 286) may be updated withthe information representing the orientation and progress of the drillbit. Referring specifically to FIG. 24, an embodiment of the circularchart 286 of the display 250 (FIG. 2B) is illustrated with differentlypositioned circles than those shown in FIG. 2B and may be used to showthe orientation and/or mechanical progress of the drill bit at surveypoints and/or between surveys. More specifically, FIG. 2B illustrates aparticular positioning of the circles ranging from the largest circle288 to the smallest circle 289. FIG. 24 illustrates a differentpositioning of circles labeled 2402 (the smallest circle), 2404, 2406,2408, 2410, 2412, 2414, and 2416 (the largest circle). As described withrespect to FIG. 2B, the series of circles may represent a timeline oftoolface orientations, with the sizes of the circles indicating thetemporal position of each circle. In the present example, the largestcircle 2416 is the newest orientation and the smallest circle 2402 isthe oldest orientation. The circular chart 286 may provide insight intowhat is happening in the borehole between surveys (e.g., usingvariations in size, color, shape, and/or other indicators). As describedpreviously, the lack of knowledge about orientation and progress betweensurveys may affect various aspects of drilling, as well as the finalefficiency of the well.

With additional reference to FIG. 25, a three-dimensional chart 2500illustrates vectors 2502, 2504, 2506, 2508, 2510, 2512, 2514, and 2516corresponding to circles 2402, 2404, 2406, 2408, 2410, 2412, 2414, and2416, respectively. The vectors 2502, 2504, 2506, 2508, 2510, 2512,2514, and 2516 are plotted against a TVD axis 2518 and compassdirections indicated by an axis 2520 representing east-west and an axis2522 representing north-south.

Each vector 2502, 2504, 2506, 2508, 2510, 2512, 2514, and 2516 providesa three dimensional representation of the orientation of the bit, aswell as an amplitude that may be used to represent the mechanicalprogress (e.g., distance traveled) of the bit and/or one or more otherindicators. The amplitude may represent a measurement such as MSE orWOB. In some embodiments, the amplitude may be a combination ofmeasurements and/or may represent the results of calculations based onsuch measurements. Accordingly, the circular chart 286 may provide agraphical illustration of the vectors 2502, 2504, 2506, 2508, 2510,2512, 2514, and 2516. Although not shown, each estimate of FIG. 16 mayresult in one of the vectors 2502, 2504, 2506, 2508, 2510, 2512, 2514,and 2516, which may be combined to provide an estimated path.

Referring again specifically to step 2304 of FIG. 23, for example, thecircle 2416 may represent the latest toolface orientation informationthat is used to calculate the vector 2516 of FIG. 25 when theinformation used to calculate the previous vector 2514 was representedon the circular chart 286 by the circle 2414. In addition, the slideindicator 292 and/or colored bar 293 may be updated to provide a visualindication of the current status of an ongoing slide.

In step 2306, a determination may be made as to whether a correction isneeded according to the information. For example, if the heading is offby five degrees, the surface steerable system 201 may identify thiserror. In step 2308, the GUI may be updated to reflect this error. Forexample, the error indicator 294 may be updated. In some embodiments,the surface steerable system 201 may correct the heading automatically,while in other embodiments the target toolface pointer 296 may change toindicate an updated correct heading. For example, as the actual toolfaceveers off course, the GUI may be repeatedly updated to indicate anoffsetting correction that should be made in cases where the GUI is usedto notify an individual for manual correction of the toolface. Althoughcontinuous or near continuous error calculations may be provided to thedriller 310, the steerable system 201 may plan a solution that usesperiodic corrections, rather than instantaneous corrections.Accordingly, the display 250 may provide the recommended corrections tothe driller 310 so that controlled, gradual, incremental step changesare made. In cases where the solution has a helical or otherwisecontinuous correction path, instantaneous or periodic corrections may bedisplayed to the driller 310. For example, the incremental stepcorrection may be a function of the tortuosity of the well, amount offriction, and/or the overall depth of the BHA. In another example, incases where the toolface is automatically controlled (e.g., via TopDrive), the method 2300 may make the correction via instructions to theTop Drive controller, via another controller, or directly.

It will be appreciated by those skilled in the art having the benefit ofthis disclosure that this system and method for surface steerabledrilling provides a way to plan a drilling process and to correct thedrilling process when either the process deviates from the plan or theplan is modified. It should be understood that the drawings and detaileddescription herein are to be regarded in an illustrative rather than arestrictive manner, and are not intended to be limiting to theparticular forms and examples disclosed. On the contrary, included areany further modifications, changes, rearrangements, substitutions,alternatives, design choices, and embodiments apparent to those ofordinary skill in the art, without departing from the spirit and scopehereof, as defined by the following claims. Thus, it is intended thatthe following claims be interpreted to embrace all such furthermodifications, changes, rearrangements, substitutions, alternatives,design choices, and embodiments.

What is claimed is:
 1. A system for drilling a wellbore, the systemcomprising: a processor; a memory coupled to the processor, wherein thememory comprises instructions executable by the processor for:determining a current location of a bottom hole assembly (BHA) in awellbore being drilled; generating a convergence path for drilling thewellbore from the current location of the BHA to a target path, whereinthe convergence path comprises a slide drilling portion and a rotarydrilling portion, and wherein the slide drilling portion of theconvergence path compensates for a formation drift of a formation to bedrilled with the rotary drilling portion; and drilling a portion of thewellbore in accordance with the convergence path.
 2. The systemaccording to claim 1, wherein the instructions further compriseinstructions for: determining an estimated amount of formation drift forthe rotary drilling portion.
 3. The system according to claim 2, whereinthe instructions further comprise instructions for: generating a vectorfor the slide drilling portion which comprises a formation drift vector,wherein the formation drift vector compensates for the estimated amountof formation drift.
 4. The system according to claim 2, wherein theinstructions further comprise instructions for orienting the BHA fordrilling the slide drilling portion.
 5. The system according to claim 1,wherein the slide drilling portion occurs prior to the rotary drillingportion.
 6. The system according to claim 2, wherein the estimatedamount of formation drift is determined responsive to drift informationfrom a previously drilled well.
 7. The system according to claim 2,wherein the estimated amount of formation drift is determined responsiveto drift information from a previously drilled portion of the wellbore.8. The system according to claim 1, wherein the instructions furthercomprise instructions for: determining a plurality of convergence pathsfrom the current location of the BHA to a target path, wherein each ofthe plurality of convergence paths comprises a slide drilling portionand a rotary drilling portion, and wherein each of the plurality ofconvergence paths compensates for the formation drift; selecting one ofthe plurality of convergence paths as an optimal path; and sending oneor more signals to a control system associated with a drilling rig todrill the wellbore in accordance with the selected convergence path. 9.The system according to claim 8, wherein the instructions furthercomprise instructions for: determining a cost associated with each ofthe plurality of convergence paths, wherein the determined cost isresponsive to the slide drilling portion and the rotary drillingportion, and wherein the one of the plurality of convergence pathsselected as optimal is associated with a lowest cost of the plurality ofconvergence paths.
 10. A method for drilling a wellbore, the methodcomprising: determining, by a computer system, a current location of abottom hole assembly (BHA) in a wellbore during drilling; determining,by the computer system, a convergence path from the current location ofthe BHA to a target path for the wellbore, wherein the convergence pathcomprises a first portion comprising a slide drilling operation and asecond portion comprising a rotary drilling operation, and wherein theconvergence path compensates for a geological drift expected duringdrilling of the convergence path; and drilling the wellbore inaccordance with the convergence path.
 11. The method according to claim10, further comprising: determining, by the computer system, anestimated amount of the expected geological drift responsive to driftinformation obtained from at least one of a previously drilled offsetwell and a previously drilled portion of the wellbore.
 12. The methodaccording to claim 11, wherein the drift information comprisesinformation from a rotary drilled portion of the previously drilledoffset well or the previously drilled portion of the wellbore.
 13. Themethod according to claim 10, wherein the first portion of theconvergence path compensates for the geological drift expected duringdrilling of the second portion of the convergence path.
 14. The methodaccording to claim 13, wherein the first portion of the convergence pathis drilled prior to the second portion of the convergence path.
 15. Themethod according to claim 10, further comprising: determining, by thecomputer system, a plurality of convergence paths from the currentlocation of the BHA to the target path, wherein each of the plurality ofconvergence paths comprises a first portion comprising a slide drillingoperation and a second portion comprising a rotary drilling operation,and wherein each of the plurality of convergence paths compensates forthe expected geological drift during drilling of the convergence path;selecting, by the computer system, one of the plurality of convergencepaths as an optimal path; and drilling a part of the wellbore inaccordance with the selected convergence path.
 16. The method accordingto claim 15, further comprising: determining, by the computer system, acost associated with each of the plurality of convergence paths.
 17. Themethod according to claim 16, wherein determining the cost associatedwith each of the plurality of convergence paths comprises determining,by the computer system, a first cost associated with the first portionand determining, by the computer system, a second cost associated withthe second portion.
 18. The method according to claim 10, wherein theconvergence path further comprises a third portion, wherein the thirdportion comprises either a slide drilling operation or a rotary drillingoperation.
 19. The method according to claim 16, wherein the step ofdetermining a cost associated with each of the plurality of convergencepaths further comprises determining a toolface vector associated witheach of the plurality of convergence paths and wherein the costassociated with each of the plurality of convergence paths is associatedwith each of the toolface vectors associated with each of the pluralityof convergence paths.
 20. The method according to claim 10, furthercomprising the steps of: determining, by the computer system, whetherthe wellbore has converged with the target path; and responsive to adetermination that the wellbore has not converged with the target path,repeating, by the computer system, the steps of claim 10.